While it is possible to replace the zipper slider yourself, it can be a tedious process. You have to use pliers to remove the stopper from the zipper, which makes it possible for the slider to come off. Then, gently remove the slider taking care not to further damage the teeth.  Next, you need to manually connect the zipper. Put each of the teeth together, watching for any bent or damaged areas that might stop the slider from moving. Once the teeth are all aligned, you may need to remove the first couple teeth from each side of the zipper. Often, the first few teeth get damaged with the stopper is pulled off. Then, you're ready to put the slider back on and re-insert the stopper.