If available some kind of fidget toy like a fidget cube. Something that can replace the feeling of chewing or biting the skin away. Sometimes rubber bands help too

I do a couple of different things! I paint my nails and use hand sanitizer alot, tastes terrible. I keep nail clippers nearby (by my bed, couch, my bag) so if there is uneven skin bugging me, I can even it out without making it worse. I also keep some of my favorite fidgets (I like tangles) and a chewable necklace with me so when I notice what I'm doing, I can switch over to one of those.

Try wearing hand sanitizer and lotion that way if you put your hands in your mouth you taste sanitizer and hopefully that’ll help you not want to put your fingers in your mouth