Depends on what kind of zipper you are trying to repair. If it is the metal kind, I carefully hold the metal piece that it goes into and using the pliers, slip it back in the slit it came out of. If the slit is loose (why it came out?) I gently squeeze it back shut with the pliers. If the metal thingie is broken, I put in a new zipper. In a pinch, I have used a safety pin through the pull thingie to use as a zipper pull.