Cut out the damaged area with tin snips.
Leave the top part of the old siding intact.
Cut out a replacement piece 6 inches wider than the piece you cut out. This allows for a 3-inch overlap at each end.
Cut off the nailing strip along the upper edge of the patch.
Apply caulk to the side and bottom edges of the cutout.
Apply roofing cement to the top edge and slide the patch into place.
Be sure to lock the bottom edge into the section below it.