the desired button could be that battery-check button, just hold it a couple of seconds and it could stop recording and starts playing the last video reversed!?
Wouldn't you use the DVR from the FPV connect on your mobile or general DVR on the goggles? It might be dangerous to have a single button on the goggles that cuts the feed. If that button gets pressed during a flight it could be what causes the crash.
Watching the video on your phone would only take a few extra seconds.