On the map or guidance view, select the Main Menu button to open the Main Menu.
Slide the volume control to change the volume of voice instructions and warnings. If the voice instructions are switched off, the volume control will still change the volume of the warnings.
Important:
For devices running on iOS 11 or earlier, the app volume control and the device volume control are linked to each other. Changing the app volume also changes the device volume and changing the device volume also changes the app volume.
For devices running on iOS 12 or later, the volume slider only controls the (relative) volume of the app (when compared to the device volume). It does not change the device volume.