To create a new video project, tap the “+” sign in the lower right corner of the app and then toggle the video slider above the record button, to put the app in video mode.
Once in recording mode you use the on-screen settings to select which camera to use (rear-facing versus front-facing), video resolution (4k* versus HD), and frame rate (30fps versus 24fps).
These settings will be maintained for any new video projects until they are adjusted again.
*4k video availability varies based on iPhone model