I couldbe way off but it sounds like a proplapse. It could be any number of organs, but most likley a hemepine.
The best this to do is to take a paper towel, dunk it in milk and wrap is around your tegus back legs. this will keep the organ from drying out and the milk will make it so the towel doesnt stick to it. Then rush him to the emergency vet so they can reinsert it.
I have heard of people reinserting them on their own using a c-tip and dipping it in baby oil then carefully pushing it back in. But i would get it to a vet. immediately.
Hope everything goes ok!
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