You may want to see your avian vet for some help.
This site goes over the issues and options really well
http://www.avianweb.com/brokenbeaks.html
Some of the problems include that the split may open more resulting in excessive bleeding. On the other hand it may grow out naturally. Beaks don't heal but they grow out (much like a split fingernail).
Do read the above link for good info on evaluating what you are dealing with.
If you do not have an avian vet as yet this site may help you find one
http://www.aav.org/search/
Hope this helps you!
Wild Bird Expert
Rehabbing wild birds, raising nestlings, study and observation of many species