It is quite easy to clean a burnt pressure cooker as long as you have the right ingredients. You will need some cream of tartar and lemon juice. Take one-liter water, add two to three tablespoons of cream of tartar in it and bring the solution to boil. Add about the same tablespoons of lemon juice and turn off the heat. Pour this solution into the instant pot and leave it for at least 15 to 30 minutes. Scrub the pot using a cloth or a sponge, and finally rinse it off. The instant pot will be as good as new.
https://instantpot.wpengine.com/faq/