It may be illegal, yes - but it was a generous act. And yes, some do carry Salmonella and have respiratory problems. The tortoise should not eat lettuce, coleslaw, or anything along that line.
First, put him in a shallow container of lukewarm water to make sure he is clean and expels the waste. Tortoises urinate and defecate in water, so you will need to let him do his thing, then give him a clean container about once or twice a week to go in on his own. Also, provide a separate container to leave in for it to drink out of.
They eat (all shredded) fresh kale, shredded carrots, collard, turnip and mustard greens, green beans, sweet potatoes snow peas, some types of fruits. They also have tortoise food in a pet or feed store, but I would recommend making your own salad of the above. You can make most of it in advance and if you have access to fresh clean grass or alfalfa grass or pellets. They also eat some dead plants and weeds, just double check to make sure they are not poisonous. They also need sunlight or an UVB florescent light if they cannot get the real thing. They also have vitamins that will help greatly.
Good luck and when in doubt, ask Google or go to a tortoise site for help. I had been raising a desert tortoise for 5 years (15 years ago) that was a hatchling and covered in red ants when my husband found her. But when she had to go to a forever home (landlord issues), she was given a perfect health checkup from the new mom's vet. I still miss her but know she is with other tortoises and should be having good her own babies by now.
The tortoise will eat when she is settle in her new home and after she goes to the bathroom. They only eat maybe once a day really good. Some only once a week. This is the time they are coming out of hibernation and she may have already eaten. Best to not handle her and let her be to get settled in a while. Just keep feeding and giving her fresh water on a daily basis.
Again, good luck.
