Start by removing the old zipper slider off the zipper. To do this, bring the slider to the top of the zipper. You can use a seam ripper to remove fabric stitching if needed. Make sure you remove ...

Remove the metal "stops" at the top of the zipper using pliers, and take off the slide. Now you can realign the teeth manually. Put the slide back on, and reattach the top stops. If you're not ...