Ok, I'd wait until all the others hatch. Normally when a chick finally makes that final zip and kicks his way out, his yolk is totally absorbed.
If it isn't, the mortality rate is high. In other words, the chick knows when his yolk is absorbed and makes that final push out into the world...
So all the other chicks hatched? If nothing happens within a few hours I'd help it out. If you could carefully see if the yolk is absorbed or not, that will tell if he's ready. I'd still put a damp warm paper towel over the hole. Let us know about movement, sound, etc.
I'd give it some time as the chick takes long rests while trying to hatch. A damp (not dripping!)paper towel with warm water to cover the hole...just laying over it. I'd check every 15 minutes.