Ok, gather up some supplies; tweezers, paper towels, warm water, bacitracin or Neosporin without pain medicine, q-tips.
All I do is, with a pair of tweezers, start breaking off tiny bits of shell towards the air cell. Be very mindful of the membrane and keep an eye out for blood vessels.
The blood vessels are very delicate and just barely tapping them with the tweezers can sometimes cause them to bleed. If the membrane is white, you won't be able to see the blood vessels.
Work in increments of 5 minutes. If you see any bleeding, apply some pressure with a q-tip until it stops. Before you put it back in the incubator, use a q-tip to wet the membrane with Neosporin or bacitracin. Wait an hour, then remove a bit more of the shell.
Take your time!
I have to go to a meeting, I'll be back in an hour or so...