Certified GKH Gardening Expert
As long as you did not girdle the tree (cut the bark all the way around), it should recover on its own.
If you did girdle it, they is not much to be done, though you can try this method as a last ditch effort:
If you have any other young trees in your yard, try putting a slitted piece of plastic tubing around the base until their bark toughens up a bit. This will help prevent damage from weed whackers or other objects that could cut the bark.