Q&A for How to Sew in a Zipper

Yes, it's possible. Cut the teeth off the old zipper, and sew the new zipper onto the protruding tab from the "toothless" old zipper.

Add a 1/2 inch on both sides of fabric to allow enough fabric for the zipper. It does work even if zipper is supposed to be hidden. Practice on another piece of fabric first. I did this on a nice dress I like, as it had no zipper and I needed a front zipper for easy access, as I am a cancer patient and needed to get my arm in without lifting it. The zipper is hidden into a seam.

Pin the zipper in the right place to prevent the material from moving and stretching.

You can do this by pinning it in the place that you want to put it once you have stitched up all the sides.

Get scissors, a pointed knife or a quick-unpick. Find a stitch near the start of the thread you are trying to remove. Push the blade between the fabric and the thread, with the sharp edge against thread. Pull up carefully to cut the thread. Move to the next stitch and repeat the process. Pick off the loose thread pieces.