OK first up..He does not need to eat right now. He can stay in the bator for up to 48 hours after hatch without eating or drinking. If he has not absorbed his yolk there is little chance he will survive. You can not pull off the sack it needs to be absorbed by the chick. I would try wrapping the part where the sack is still attached to the chicken with a moist cloth. I would have not intervened on a chicken that has not hatched for only 12 hours. Some of them can be quite slow hatching up to 24hours can be very normal from pip to hatch. When you open the incubator while they are pipping you mix up the humidity and they will quite often get shrink wrapped.