Issue - There's damage to the zipper on a backpack.

Technique - Isolate each slider to one side of the damage so the damage location will become the place where the sliders meet.

Use the skill in Steps 9 and 10 to refasten the zipper teeth on both sides of the damage.

Use the skill in Step 11 to retrack both sliders onto the zipper at the damaged area.

Place a coil top stop at the damaged area with the sides of the zipper either together or apart depending on preference.