First, this isn't one of ours.
Once a metal zipper gets like this it's almost impossible to get the teeth to realign because you can't go backwards easily on a separated metal zipper.
Best is to find a shoe or luggage repair to replace the zipper if it's broken or to realign it if the zipper teeth are fine.
You can also try Zlide-On which is a snap-on slider replacement. Google them and you will find where to get it.