It will grow back but it depends on how much damage was done to the under laying tissue rather or not it will be useable. Put anti-biotic ointment on the beak and feed him from a deep cup with a lot of feed in it, more than he can eat so he has a cushion to peck into. Isolate him from other birds so they don't bother him.
If you had the broken beak it's best to tie it back on for a few days but of course if you knew how to do that you wouldn't be asking. Also tieing it on is a difficult skill to learn. Maybe you can find a video on how to do it for the next time.
"the time will come, that who killeth you will think that he does God service." John 16:2
Apply furacin cream. Rub it gentely untill cream is aborbed. Feeding on a soft cloth tied on top of a deep bowl (so that its beak does not touch hard surface at the bottom of bowl) is a good idea. As Bull-god suggested if you find beak cover tie it back. If you don;t find his own tieng another bird's beak cover will also help grow the tissues underneath safely. I heard horse hoof polish also works wonder but have not tired it yet.