The lisp is a functional speech disorder, or a difficulty in learning to form one or more specific sounds of language. The term "lisp" itself is a profane term and is not used by most speech therapists. The lisp is characterized by difficulty in pronouncing the sounds / s / and / z /. For example, the words "soup" and "shoe" might sound like "thopa" and "thapato". The most common types of lisps are interdental and dental, which are also known as frontal lisps. The sounds / s / and / z / are produced either with the tongue protruding between the teeth (interdental), which results in a / th / sound, or with the tongue touching the teeth (dental), which gives as a result a muffled / th / sound. These two common types of lisp are considered normal parts of language development in children and should not be seen as unusual for children under the age of 4 1/2. In case you have a lisp, here are some tips to correct your pronunciation.
Steps
Part 1 of 3: Pronounce the sounds with a mirror

Step 1. Smile
Look at yourself in the mirror and open your lips as if you are smiling. When you begin to pronounce the sounds, you should keep your lips open in this way so that you can see your teeth at all times.

Step 2. Close the teeth and align them
Align your teeth so that the bottom row is just below the top row, lightly touching. Hold them against each other like this. If you have a slight natural overbite when smiling (this is the case for many people), it will be necessary to move your lower jaw forward a little so that the teeth are in the correct position. It may stop looking like a genuine smile in the mirror, but that's okay.

Step 3. Place your tongue in the correct position
Keep your tongue back away from your teeth. It should be around the center of your mouth, slightly back and just behind your upper teeth. It should not be stuck to the palate. Otherwise, the air will not be able to break through to produce the sounds.

Step 4. Practice the sounds
Practice saying / sssss /, like you're hissing like a snake. To do this, blow air through your teeth while they are aligned as explained above, taking care to keep your tongue back away from them. Do this several times until it sounds like a clear / s /.
If you want to practice / z /, keep your teeth and tongue in the same position but, as a speech therapist would say, "start the engine." This means vocalising a sound in your throat rather than just silently blowing air

Step 5. Ask a trusted friend or relative for feedback
After trying this method, a good way to check and make sure you pronounce the right sound is to ask someone. Ask someone who doesn't speak with a lisp, who really wants to help you, and isn't going to tease. It should be able to tell you if the sounds you produce clearly sound like / s / and / z /.
Ask him to produce the sounds as well, and try to copy what he does. Look at his mouth and teeth and try to do the same in the mirror
Part 2 of 3: Practice Vocalization Exercises

Step 1. Start with just the sounds
You will need to work until you can produce the sounds correctly while speaking naturally. Practice only pronouncing the / ssss / and / zzzz / sounds to yourself, and keep using the mirror and another person to get feedback. The more you practice, the faster you can pronounce sounds clearly when saying sentences.

Step 2. Increase speed gradually
With each step in this section, you should start slowly, and when you are comfortable with producing the sounds correctly, you can begin to perform each step more quickly. Soon, you will produce the sounds clearly at a natural rhythm.

Step 3. Try the syllables and words
Practice pronouncing sounds with syllables first. Try "saa", "see", "sii", "soo" and "suu". Then try "zaa", "zee", "zii", "zoo" and "zuu". Repeat them gradually and then quickly, trying to keep the correct sounds for the / s / and / z /.
Then practice words: sun, soup, Susana, sigh, saw, yes, sip, furrow, seven, soles, zoo, bizarre, slippers

Step 4. Practice sentences
Try repeating sentences that contain the sounds / s / and / z / (for example: "I'm going out with Susana" and "I drink seven sips"). These are other sentences you can try:
- The jumping zebra made me sneeze.
- I eat spaghetti with sauce.
- He leaves the house wearing slippers.

Step 5. Repeat tongue twisters
After you can say clear / s / and / z / sentences quite easily and quickly, try some tongue twisters:
- If Samson seasons his sauce without salt, it turns out bland.
- If a hundred saws saw a hundred cypress trees, six hundred saws saw six hundred cypresses.

Step 6. Don't stop practicing
Changing the way you've been speaking can take a bit of work. Avoid giving up if you don't see results right away. Practice the techniques for at least 20 minutes a day. Ask your friends and relatives for feedback as to whether or not they think you improve your pronunciation during conversations.
Children in schools often participate in speech therapy for months or even years to improve lisp. If you don't see any improvement in a couple of months, try reaching out to a speech therapist for further assistance
Part 3 of 3: Strengthening Your Mouth and Tongue

Step 1. Drink using a straw
Using a straw can help build oral strength by strengthening the tongue, as it needs to be pushed back when drinking. So, get some straws and put them in glasses, cans, or bottles when you drink something.

Step 2. Blow into a round nozzle
Blowing of any kind, whether through the mouthpiece of an instrument, a whistle, a horn, a kazoo, etc., helps to strengthen the muscles in the mouth area.
You can also blow bubbles. It's certainly for kids, but it can also be fun for adults, and if you have kids or nephews, they'll love doing it with you

Step 3. Practice the sounds with the tip of your tongue
Say "lalalalalalalala" without moving your jaw up and down. Just move the tip of your tongue. Rest and repeat.
Do this with other sounds with the tip of your tongue (for example, "tatatatatata", "nanananana" and "dadadadada"). Any sound that makes your tongue move quickly will help strengthen it

Step 4. Click your tongue
Suck your tongue up against the roof of your mouth for 1-2 seconds and then flick it. Try to get to 25 reps. Exercising like this should gradually make you feel more in control over your use of your tongue. This will help you when you speak so as not to produce confusing sounds.
Advice
- Ask a speech therapist for help if you still have difficulty forming sounds clearly or if you still speak with a lisp after practicing despite your best efforts.
- Just relax. In many cases, speech disorders become more apparent when someone is anxious or nervous. In case you accidentally lisp when speaking, try not to embarrass yourself. This is part of who you are and there are quite a few celebrities who have had a lisp. While it's understandable that you want to change it, this can be a slow process, and for the most part, people can't do it overnight. So, be patient and be kind to yourself!