as long as it does not tear it open it will heal up and be fine. I personally would put it in a smaller area so it can't tear it open on a damp paper towel like MC said
I don't think that's actually on the chicks vent but instead it is where the yolk Sac absorbs. It looks like an incomplete absorption of the yolk sac. Keep it on something soft so it does not tear it and it should go away over the next 12 to 24 hours