This isn't an exact science I'm afraid. You just need to watch to ensure the membrane remains moist and see if the chick begins to progress on its own. If it doesn't show any signs of that in a couple of hours but is still peeping and moving and seeming vigorous, then you could try chipping the EGG SHELL away for it, leaving the membrane intact and only removing it from the 'lid' of the egg....where the chick would naturally zip around the air cell. Do it bit by bit and then return the egg to the incy to see if it continues under its own stean HOWEVER every time you interfere with this one, all your other eggs are at risk from the drop in temperature and humidity so its also a judgement call....is the life of this one worth potentially sacrificing the life of the others for?
I wish there was an easy 'one size fits all' answer for you but there just isn't. We interfere with nature by using an incubator, often causing problems that may not have arisen naturally and then we are left with difficult choices as to whether we should attempt to put them right and if so, how and when.
Put in a search for assisted hatches on here and you will find lots of info but much of it will conflict and you will need to choose which way to go.
I wish you the very best of luck.
Oh and please do not think I am criticising in any way, I had a hatch 6 days ago and had to make the same decision....I assisted, got a very malformed chick and have spent ever since giving her intensive care.....but she is now thriving and running around with her siblings like it never happened so my decision turned out well in the end....but it could so easily have gone the other way or resulted in a need to cull the chick I so lovingly helped out!