I've helped many shrink-wrapped chicks (though I'm by no means an expert
). This is how I do it...
With the tweezers, I "zip" the shell for him. I also tear the membrane all along the zip, except for about a quarter of it (assuming that it's still moist enough for the chick to tear it*). Then, I put it back in the bator (being very quick while opening the bator of course). About an hour later, when I check it again, it's hatched the rest of the way. One VERY important thing I've found, is the chick needs to push and struggle. If it's too easy, then he will be a weak chick, usually dieing within a day or two. So, while I'm working on him, I do it rather slowly, and every half minute or so, scratch the shell, which makes him push.
*If the membrane is dry all the way around, then I go ahead and take the top half of the shell off. After checking that he's not stuck to the bottom part of the shell with dried membrane, I put him either in the bator, or in the brooder in his own little "pen." Do NOT remove the bottom part of the shell, just leave that to him.