Just go to to dealership tell them to estimate it. Ask them to use cutting (I heard the term there) first to see if it goes away or fades. Depends how big and visible the scratch is. If it is not visible six feet away leave it. Else you will have to call insurance.
If car is less than six months old, you will have to pay 5 percent, if more than six then 10 percent of the cost of complete repaint of the bumper. Will take at least three days, they may ask you to leave the car in paint shop or just remove the bumper.