To adjust the LifeMix level, you'll need the Dolby Dimension Mobile Application.  Once connected press 'Manage LifeMix/ANC' on the main screen. From the LifeMix page, you can scroll up or down to set the desired level.  Scrolling to 0 will turn off LifeMix and turn on ANC.  A double tap on the LifeMix page will toggle LifeMix on and off just like double tapping the right Control Plate.