Check for fabric or thread caught in the zipper teeth
Gently pull the fabric free with tweezers
Rub a graphite pencil, soap, or zipper lubricant along the teeth
Move the slider up and down slowly to test it
If the slider is loose, gently squeeze it with pliers
If the teeth are misaligned, realign them by hand
If a tooth is bent, straighten it carefully with pliers
If the zipper separates, replace the slider
If the stop is damaged, replace the top or bottom stop
If the teeth are broken, replace the entire zipper