You can mist his cage and bump the humidity even higher for a day or two. You could also try soaking him in 85 degree water for around 30 minutes. No more than an inch of water - it should only come half-way up his body.

It's difficult to help them when it's stuck on their head because they usually spaz. Hopefully if you give him enough humidity he'll do it himself. Also make sure he has a rock or something rough to rub against. They can do their bodies just by rubbing their coils together, but they have to rub their heads on something to get that off. That may be the problem.