I too would replace the zip. Or have a dry-cleaners/alterations-tailor replace it for you.
It'd be a good idea to source a replacement zip first. The correct size, colour, quality... so they don't fit an inferior one.
If your zip is intact but not meshing, i.e. the teeth are open in front and behind the slider, there are some good YouTube videos showing how to fix that.
A light spray of dry Silicone Lube (for bike chains), or Paste Furniture Wax, work well to keep zips running smoothly.