I accidently touched something on my Phantom 4 Pro Plus screen while I was flying that made everything disappear except the video. How do I get it back without restarting the controller?

Swiping down or up with one finger on screen usually takes my iPad in or out of full screen mode, so try that on your screen. There may be an option to set it as two finger swipe required to reduce chances of accidental activation.

Hello there, it seems that you entered the full screen accidentally. Please try to swipe down with Single Finger/Double Fingers to exit. You can also set Single Finger/Double Fingers in General Settings>Full Screen.