If the switch is on (default option), the microphone button appears at the bottom of the main screen; click on it and announce the new speed limit.

If it is off, the button of micro disappears from the main screen and the speed limit change can only be done by clicking on the gear buttons.
If the switch is on, voice recognition is done offline, for this the language pack must have been downloaded.

If it is off (default option), speech recognition is only done via mobile data.
If the switch is on (default option), after voice recognition, the speed is announced via the audio device.

If it is off, speed is not announced after voice recognition.