Baby with huge umbilical still attached

[Rhondax6]

She was hatched yesterday, clearly a little distressed. what do i do? we've already lost most of the hatch because the mother hen is clearly a bird brain.,

 

[Rhondax6]

I assume its the yolk sac...... Ive been reading to keep her damp and warm so I'll try that and hope we don't lose another.

eta burst yolk sac