Press the fan symbol in the bottom bar 
.
.Press the rear defroster symbol 
.
.Tip
Overhead console defroster button
The defroster button 
in the overhead console activates max defroster as well as the heating of the rear windscreen and wing mirrors. If you already have either the max defroster or rear defroster activated via the centre display, pressing the defroster button in the overhead console will activate the second function. Press the defroster button again to turn both off.
Automatic rear defroster
In climate settings, you can set the rear defroster to automatically turn on when you start the car in cold conditions.