It should turn back to normal after a while. If it has been a day or several hours since the rubber band was removed and is still red and swollen then see a doctor something is wrong.
My child left a rubber band on her hand and now its red and swollen what do i do?
Remove the rubber band and press it with warm water and leave her hand bare for a few days. If the swelling has not go down, take her and see a doctor.