There is a product called “vapona” it’s a no pest strip that is effective for killing all kinds of bugs including mites. It quite toxic so you need to make sure you have good ventilation and put it in some kind of container to keep the snake from coming in direct contact with it, a empty margarine container with a bunch of holes punched in it works just fine. I’ve used it years ago very successfully for treating mites but like I said it’s pretty toxic so I wouldn’t use it unless you’re sure you have a mite problem, and don’t leave it in the cage for more than a week or so.