That can be caused by coming out too early, or it's a genetics. If you tried pulling the chick out of the shell; that can cause it to. Chicks like that, actually cannot survive, but it's difficult. You have to make sure that their environment is moist enough. And that you have to keep it (that part of the chick) from drying out. So you have to add warm water to it on occasion. And all you can do is just wait-and-see. It might take A few days for it to go back in. If it doesn't then the chick might not survive. Or will survive, but it will be extended, and it won't live properly.