Hey, I found this procedure on the internet, and it might go a long way to help you overcome your condition.
For this procedure to be successful, you need a family member or friend you can trust not to tickle you in the course of the procedure just for the fun of it.
Find a very serene and private place where you can relax on a bed, couch, or floor with your feet exposed. I don't know why, but over the years, I have discovered that it works best to begin with the feet. Sit with the person assisting you at your feet, with your knees in a bent position to enable you tickle your own feet.
This step will require a level of patience, time and focus. You may have to carry out this particular step repeatedly before you get the required results.
The whole basis of this procedure is that you can tickle yourself, just like we learnt as kids. The fact that others can tickle you while you can't tickle yourself shows that it is a mental issue.
Begin by tickling your foot, one foot at a time. Continue the tickling for about 10 minutes or until you get tired of doing it. Then let your assistant help you with the fourth step.
Your assistant is expected to place a fingertip on the bottom of the foot you are tickling. Continue the tickling during the entire step. Your assistant's finger placed under your foot must not be moved around. Once you start giggling, make efforts to fight the sensation. Remind yourself that you are not being tickled-it is only an immobile finger under your foot. This will make it hard for your brain and foot to differentiate between your assistant's one finger and your eight fingers. Once you are able to resist the urge to giggle with your assistant's finger on your foot, you can proceed to the fifth step.
Now it is clear to you that you can have another person's finger on your foot without giggling-let's proceed. This fifth step also requires you to keep tickling yourself.
This step requires your assistant to move his/her one finger with your eight fingers along your foot bottom. This is where you work on your mindset by convincing yourself that there is no difference between your assistant's finger and any of your eight fingers. This process continues until your assistant can move his/her one finger at the same pressure/speed you were moving your eight fingers. Once you can avoid becoming hysterical with laughter at this stage, it shows you are doing great, and it is time for the sixth step. But if you couldn't control your laughter with your assistants finger moving up and down your foot, repeat step five again.
Since you can bear the touch of your assistant’s finger on your foot even with the movements, we can now increase the number of fingers. Now your partner should be tickling you with two fingers while you tickle yourself with eight. This will continue until your partner's eight fingers are moving along the foot with your own eight fingers. The trick here is that with sixteen fingers crawling up and down your foot, your brain won't be able to distinguish between yours and your partner's. The success of this will depend on your mental ability to adapt. It may take a number of sessions, several attempts, and an extremely patient assistant.
Once you can endure your assistant's eight fingers and your eight fingers tickling you at the same time, it is time for the seventh step.
You have passed the difficult stage-congratulations!
In the seventh step, you will withdraw your fingers from your foot gradually while your assistant's fingers continues the job of tickling you slowly and methodically. It is important to choose an assistant that won't break your concentration by tickling you in a way that makes you laugh out loud.
Every step is important, but this step is most important because the goal is for your assistant's finger's to be the only ones tickling you. This step should be repeated a number of times to enable your brain build the necessary synapse connections that have never been there. Your brain needs to get used to another person's fingers tickling you without you laughing uncontrollably.
Repeat each of these steps as many times as you can until you can stand your partner's fingers tickling your foot without you rolling on the floor with bouts of laughter. Once you can control the urge to laugh with your partner's fingers caressing your foot at higher frequencies and pressures, you can try other sensitive parts of your body.
I sincerely hope you find this helpful on how to not be ticklish.
Good luck to you!!