I have the same problem. There doesn’t seem to be a way to reset all the DVR settings. Now stuck.
This isn’t good, as I am evaluating Plex DVR vs. other similar products and it’s let me down. I have potential users waiting on my findings.
Update: Solved by going to Plex console though its local IP address, e.g. 192.168.x.x:32400
Time will tell if it’s going to be reliable though. This is not a good start.