Use a keyring or a small paperclip as a temporary zipper pull. For a permanent fix, swap the broken pull tab with a new one by sliding it into place. Squeeze it closed gently with a pair of pliers.

Got a broken zipper box? You can fix that with 3D printing. Mystified about how zippers work? No need to be.

You're on your way out the door, you grab your coat, and the zipper is stuck or broken.