You can pry open a large metal zipper slider with a screwdriver and press it closed over the zipper with pliers. Replace plastic slides, small metal slides and missing slides by removing the top stop, inserting a replacement slide onto the zipper and attaching a new top stop.
To repair a metal zipper slide, pry open the slide by inserting the screwdriver into the sides of the zipper and twisting or pressing down on the screwdriver. Attach the slide to the bottom of the zipper and align the zipper teeth inside the slide. Press the slide closed with pliers a little at a time and test the zipper several times until the slide moves smoothly.
To replace the zipper slide, pry the top stop off of the zipper with pliers. Remove the old zipper slide from the top and back a new slide from a zipper repair kit onto the zipper. Some metal stops can be reattached to the zipper, or a new stop can be pressed onto the zipper with pliers. Some replacement zipper slides do not require tools to attach to a zipper. The replacement zipper slide by FixNZip.com uses a built-in screw to open and close the slide over the zipper.