This has happened to us a couple times but we thought it would be useful to take pictures of what we have done.
We first started by cutting the top half of the egg off to make sure that we couldn't do anything to untwist it without taking the snake out of the egg. Once we knew it was twisted and we couldn't untwist it we carefully pulled the snake out of the egg.
Once we got it out we got a better look, and you can see by the pictures that it wasn't able to be untwisted.
We then got some dental floss and put it under the Umbical cord, then tied it off, we put two knots in it so it wouldn't come loose.
After we tied it off we cut the rest of the yolk sack off, we made sure to cut it on the left side so that everything stayed in.
Thats pretty much how you cut the sack off, after we cut it off we put it on wet papertowel (it's really important to keep it as moist as possible.) We then took a syringe and sucked up some of the yolk, then fed it to the snake so that it had something to live on before its first meal, which will most likely have to be assist fed until it starts eating on it's own. Hope this info is useful for everyone