I just had to do the same with one of my young pullets a couple nights ago. Her upper beak had gotten far too long and had begun to split as well. I used large nail clippers and trimmed it to a much more comfortable length (for her). You want to watch out that you don't clip it too close to the quick and you should be fine. One thing you can do to help prevent this is provide them with concrete or cinder blocks or large rocks that they can scrape their beaks on. I have them scattered about and mine use them frequently. Don't know why this girl didn't. First time I've had this issue.I have a hen that is about 8months old and she is rubbing her beak along the chicken wire in her hen house. It is now starting to split on the end so i trimmed a little with toe nail clippers i don't want to trim too much, but it is still split. Any suggestions?