You can activate the rear windscreen and wing mirror heating via both the centre display and the button panel below the centre display.
Activating via the centre display
Press the fan symbol in the bottom bar 
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.Press the rear defroster symbol 
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.Activating via the button panel
Press the rear defroster button 
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.Tip
Automatic rear defroster
In climate settings, you can set the rear defroster to automatically turn on when you start the car in cold conditions.
Press 
in the climate view and go to Auto rear defroster.