I was using FloleVac Android App as per this post.
Basically you go to Zone Cleanup, paint the zone on the map and long press on Start, it will copy the coordinates to the clipboard.
Be absolutely sure the coordinates are reachable otherwise the vacuum will return to the dock or not even start at all, it will come out of the dock wait a few seconds and go back to the dock.
It could even be a few centimeters that are unreachable but because of that it might go back to the dock.