Okay if the membrane isn't brown and dried looking then maybe just put it back, if you think it's dry you might take a sterile pair of tweezers and just barely make a hole by pulling on the membrane. once you get that hole in their put the egg back under mom and leave it alone because every time you pull the egg out humidity is dropped and can cause the membrane to dry out too much and the duckling can't get out.
Just pour some rubbing alcohol over the tweezers to sterlize them
sorry I had to go let my flock out for the day.