Check for fabric, thread, or debris caught in the zipper teeth
Remove any visible obstruction with tweezers or a small tool
Clean the zipper teeth with a toothbrush or soft brush
Apply graphite, zipper lubricant, or a small amount of soap to the teeth
Move the slider back and forth gently to work the lubricant in
If the zipper is separated, align both sides and reinsert the slider if possible
Use pliers to gently tighten a loose zipper slider
Replace a broken zipper pull with a key ring, paperclip, or cord
Realign bent zipper teeth with small pliers
If teeth are missing or the slider is damaged, replace the zipper slider
Sew or patch torn fabric near the zipper to prevent snagging
Test the zipper slowly after each fix
Take the backpack to a repair shop if the zipper is severely damaged