I chipped a bit of the shell away, just enough to expose the beak, and dabbed a bit of olive oil on the membrane to prevent it from drying out while being handled.
If it doesn't manage to unzip by morning I'll assist further.
My plan was to just remove a bit of the small end of the shell so the chick could work on getting out. As soon as I removed a small chuck of shell over its head it leapt out of the shell .
Everything looks okay. The yolk has receded and I removed a bit of membrane so it won't dry on the chick and cause issues. The belly button still pokes out a bit, but it should go down over the next few hours.