There are threads that address these issues, I just couldn’t find the one I read few months ago from one guy that has excellent guide on assist hatch. Check sally sunshine’s post she has a lot of good stuff.
Though I assist a couple of hatches and they were very successful, I am not confident enough to give such instruction, though personally I will do it again if need so. My first assist was with an egg that pipped over 30 hours but couldn’t zip, the exposed membrane are drying out and was longer than expected. I carefully peel off a few of egg shells around the pip hole and use warm water (some people use Vaseline or some kind of oil) to moist the exposed dried membrane and continue on as long as there was no blood vessels injured that can cause bleeding. I’ve used a tweezer and a surgical scissor to do the job, made sure that the egg yolk been absorbed so I continue on, and put back the hatched chick in the incubator to dry and fluff and rested, that took 6-8 hours. Later on discovered that the chick had trouble with spry leg so I taped them and she was able to stand and walk, removed the tapes a day later and she was normal as can be.
The 2nd time I had to assist was last week when one of my Olive Egger egg in a different incubator, seem to pipped on the wrong end it also been the 2nd day. This time I had to feel off very carefully since I don’t know where the beak was, end up was behind the wing cartilage, the reason it’s having hard time coming out, since each time it pecks out it peckS on its own wings. I also used warm water for moisture on the shell and membrane then I exposed the beak and head and let it finished it’s own hatching which probably took 6 hours when I came back from work.