Check whether the zipper is stuck, misaligned, or missing teeth
Apply graphite, soap, or zipper lubricant to the teeth
Gently wiggle the slider up and down while keeping the fabric straight
Use pliers to slightly tighten a loose slider
Replace a broken zipper pull with a paper clip or key ring
Reinsert the slider if it has come off one side of the teeth
Sew a few stitches above the bottom stop if the slider keeps coming off
Replace missing or damaged bottom stops with a new stop or stitches
Replace the entire zipper if the teeth are broken, bent, or separated
Test the zipper several times after repair
Take the trousers to a tailor if the zipper cannot be fixed at home