During your flight if the aircraft runs out of batteries, the flight's battery timer has expired, or the user presses the Return to Home button the app will draw a blue dot on the flight path called an Abandonment Point. The app will allow you to come back to this point to restart.
If for some reason you don't have an abandonment point to go back to you could always use the Manual Restart Point feature which allows you to go back to the start or end of any pass directly. This can be done during the path verification step that shows you the blue line before taking off.
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