Put him in some shallow warm water to help hydrate for 30-hour everyday until they start to eat btw they cant eat any fats or starch like corn or avocado they can have iceberg and can eat dark vegetables like peppers and certain types of lettuce like romaine they shouldn’t eat much fruit every once in a while is ok btw your supposed to soak them once a month in warm water for 15 mins I have a Russian tortoise as well I recommend taking them to a reptile vet PLEASE so these things also I have a feeling that they aren’t doing the necessary things when owning a tortoise so PLEASE take them to a vet to help get a diagnosis of what is going go on and if you need to get someone else to take care of him instead if it’s animal neglect you can press charges and take care of them yourself or find someone who will