Are you using prolapse correctly? as in its anus or sexual organs are hanging out side of the body where they shouldnt be? If so, there are a few things to consider.
First I'm going to say I've never actualy had to deal with this problem, I've only read about it and its solutions. First Is there any signs of parisites, specificaly worms? If yes treat outside of your main tank for internal/external parisites (though its a puffer so I guess treating in the main tank wouldnt be that big a problem due to the complete lack of inverts for the copper to kill haha), as sometimes this can be caused by parisites. Also has his diet changed resently? as changes in diet can sometimes be hard on there system.
Not a bad to treat with a antibiotic if you can, I suppose dabbing it on...? not sure Id have to look that up.
But in any case DO NOT try to push it back in for any reason this could cause more problems and possibly kill him, if its going to heal it will heal otherwise not much you can do but what I mentioned.
