Hi
Please note I am a beginner but here is my experience.
We had a home made incubator in which I think the humidity was too low (always around 35-40% never at 60 or 70%).
We had 11 eggs and 7 hatched, all on Day 17 (when Coturnix are due). They started pipping on the evening of Day 16, by the afternoon of Day 17 four got out by themselves and but three needed help out the eggs as i think the membranes were drying too quickly. (Upon post mortem we found three weren't fertile and one fully developed chick never even pipped so I am not sure when it died or why).
So, helping chicks. For those who had pipped and had made a gap but were making no progress, I helped by VERY delicately chipping some shell away being careful not to damage the membrane (as there are blood vessels in it that can be still attached to the chick). They were then able to kick their way out, however two I also had to help through the membrane (only where there was clear movement underneath so I could tell they had separated from it).
All 7 are alive and doing well one week on, but please bear in mind it was a very delicate operation and you should never tear the membrane from the chick. Everyone will also probably say I should have left them, but I couldn't help but feel it was our environment causing their struggle as opposed to their inherent weakness, so I felt duty bound to help. But that's just me as I can't stand the idea of them being trapped because of us. So maybe judge if your situation is similar, I wouldnt hesitate to do the same again, though next time I will be making sure the humidity is much higher.