Rub the mirror with toothpaste the abrasive ingredients can buff the scratch out if it is minor.
Front or back?
If deep its there to stay. Sorry
Hi Tracy. You can fill the scratch with clear nail polish and it will disappear. Good luck.
If you need to fill the scratch you can use clear epoxy. After it cures use a single edged razor blade to remove any epoxy that is above the mirrors surface.
Here are some common household repair methods: