The speed limiter must be enabled in settings before it can be activated.1
When it's safe to do so, press the speed limiter button 
on the steering wheel.
Activation is confirmed in the driver display.
The first time you activate the speed limiter during a drive, your speed at the time of activation becomes the set speed limit.
If you have enabled the automatic speed limiter it will adapt the set speed limit to that of the road you're on.