Something is saying Egypt in the back of my mind (but no logical reason, just a guess?)
What ever species it is I would say the basics are keep him well hydrated. In practical terms this means placing him in a container he can fit completely in & stretch out comfortably in. Add warm water 30-35 degrees up to his first row of scutes (tiles on his shell) leave him approx 30mins, longer if he will sit happily (you may need to top up the water with warmer to keep it warm)
The other thing he needs is warmth, preferably from above. Could you set up a light bulb (any approx 12inches/30cm above his shell to give a temperature of about 30 degrees C. He must though be able to move away from the lamp if he so wishes.
I would confine him in a container of some sort. As if he isn't used to a lamp + he's not feeling 100% he will probably shy away into a quiet corner to hide.
We can discuss UV etc later. Food wise I would maybe offer a little of what he is used to but chop it up. This will make it easier for him to take small pieces but also release aroma & flavour, attracting him to eat it. Even if he doesn't eat for a while hydration is far more important, so keep soaking him.
Anyway I hope this will help. Please let us know how you get on. Good luck
x