To activate them:
1. Turn on the rear window defroster. This is typically a button with a rear window icon, often located on the center console or near the climate controls.
Once the rear defroster is on, the heated mirrors will automatically activate as well. You won't see a separate light or indicator for the mirrors themselves. If they're not working, check the rear defroster's function first. If that works, the mirror heating elements may be faulty.