I agree with the above posts about leaving the chicks in the incubator and seeing if the yolk absorbs. If it does not, then you have a two person job.
Get ready sterile saline or boiled cooled water with a pinch of salt, lubricating jelly and a Band Aid, finger size or porous tape e.g Micropore.
One person holds the chick steady. The other person makes sure that the nail on the little finger is very short and then washes hands thoroughly, wears gloves pr uses hand steriliser.
Make sure that the yolk sac remnant is free from bits of eggs shell, or dirt. If anything present carefully remove it with a gauze pad dipped in saline. With the tip of the little finger dipped in sterile lubricating gel, very carefully and gently reduce the yolk sac remnant through the hole (if the hole is very large the chick is unlikely to survive). Once everything is inside place the Band Aid or tape across the defect and leave it there.It will eventually fall off and only needs replacing if there is a scab that that others may peck.
This can be very successful and I have had a number of 'plaster bums' who have made healthy adults.
Good Luck,
Sandie