Depends on how far it has progressed, if only piped leave it be, if fully or mostly zipped for 12-24 hours and if it's still not out I would see is it's stuck to the membrane or in an odd position. I assisted 1 chick by wrapping a warm paper towel around it and placing it back into the incubator. I let it sit for about 30 min (to avoid chilling due to moisture) then removed paper towel, and gently started to open the "lid" created by zipping. then placed her back into the incubator. My chick was stuck to the lid and had not fully zipped, I think it being under the fan dried it out too quick and it got stuck while turning to finish zipping. I also made the mistake of removing chicks to place them in the brooder too often, thus lowering humidity. Good luck!
40% should have been good, when you candled how did the air cells look? This is your best indicator for humidity requirements. If the are small you need less humidity, if the are overly large you need more. There are a ton of diagrams but really if the air cells are approximately 20% of total egg you are on the right track. If you have eggs with small air cells and you raise it too high, 75-80%, then you increase the chance of those cells holing water that can drown your chicks. From my reading this would be the time to keep moisture closer 55% as the eggs themselves will contribute the rest of the needed moisture. And vice versa, if the air cells are over 30% of the egg you need to get that moisture closer to 75% and hold it there. Any experts feel free to correct me, this is only my understanding of the process, and it worked well for me.
Several people have said wait till day 25 but be vigilant about smells/oozing so you do not have anything explode in there. If temp.s ran low they can take longer to hatch.
