I just had to assist a 'stuck' pheasant chick...I usually don't assist but it had zipped part way and became stuck, the shell was unusually thick and the chick was becoming weak.
Try chipping the shell off in a manner similar to the chick would when zipping. Go slow and if you encounter any veins or blood, STOP. Put back in the incubator and check back on it in an hour or so, if no veins or blood is encountered, continue until the shell is removed. Be sure to keep the membrane moist at all times, use coconut oil if you have too!