Unfortunately there isn't much you can do now. Just like when you touch a hot stove or something, the damage is already done. He is probably acting weird because it hurts like crazy!! Like Jann said, an anti-inflammatory/pain med will probably be the only thing you can do for him. But it will just need time to heal. The tongue is very delicate tissue and I worry about permanent damage that may affect how he eats.
I'm sorry, but how was he able to lick a heat bulb anyway?? And why was it not stopped if it was being observed? This is potentially a very, very serious injury.