Check for fabric, thread, or debris caught in the zipper teeth
Gently pull the zipper back and forth to free any obstruction
Use a pencil, soap, candle wax, or zipper lubricant on the teeth
Realign any separated teeth by moving the slider slowly
If the slider is loose, gently squeeze it with pliers
If the zipper pull tab is broken, replace it with a paperclip or key ring
If the zipper teeth are damaged, stop using that section and sew a new stop above it
If the zipper is stuck at the bottom, inspect the bottom stop and slider alignment
If the zipper splits open after closing, tighten the slider with pliers
If the zipper is beyond repair, replace the entire zipper
Take the backpack to a tailor, shoe repair shop, or luggage repair service if needed