It's done via the smartphone app "Video Resolution" camera setting - FOV is a secondary choice you get only for certain resolutions (1920x1080-60i and 1920-1080-30p).
You can only change the FOV for video. Still images are always a fixed width (4384 pixels). You can only change the height on still images, to get different aspect ratios. This is done with the "Photo Size" app camera setting.
