Dry spot

Before I got my adult ball python he was bitten by a rat now that spot gets pretty dry and I didn't know if I could put something on it or not

How long ago was the bite? If it's not 100% healed, it'll probably continue to look dry for awhile. A small patch of dryness won't hurt the snake, so unless it breaks open or something I wouldn't put anything on it. Old wounds sometimes have a habit of 'catching' during a shed, so when he sheds off just make sure that area is cleared of any retained bits of skin.