To fix a zipper that is missing teeth, you can follow these steps:

1. Remove the bottom or top stops with pliers, depending on where the missing teeth are.
2. Move the slider past the missing teeth and reattach the stops.
3. Alternatively, remove the tack at the base of the zipper and replace the whole zipper.
4. Or, stitch around both rows of teeth above the missing tooth to create a new stop.

You'll need a few simple tools such as needle-nose pliers and a small, flat-head screwdriver. Then, open the zipper and carefully inspect the teeth. If the teeth are bent or out of alignment, use the pliers to gently bend them back into place. Next, check the slider. If it’s broken or missing, you’ll need to replace it.

I hope this helps!