In the spring or summer and humid, I would say no, let him keep working on it. But I had three die like that in the last two weeks. It's still up to you, though. Two of the chicks I helped (one had zipped but was not able to push the top off for the membrane and the other was just pipped for a very long time) didn't make it. Others have.
If you do decided to help, use the directions I gave on the bottom of page 100, including the egg carton. If the egg is on its side, the chick may be able to crawl out too soon. Essentially, what you are doing for the chick is removing a too dry membrane and getting the poor thing more air. What you want to avoid is physically pulling the chick away from the small end of the egg, since that's where he is connected with his umbilical. You want to make it so that he can rest and then pull himself away from the shell when he's ready.