How do you fix a zipper if the slider has half come off?

To fix a zipper with a slider that's partially off, first, gently pull the slider back to the intact side of the zipper. If the slider is stuck, you might need to use pliers to carefully squeeze the sides of the slider to re-align it. Once it's back in place, test the zipper to ensure it functions properly. If the slider is damaged, consider replacing it with a new one.