To roll the firmware on the RC back, you must connect it to the PC before powering up the controller - Assistant doesn’t seem to see it if you do it in any other order.
The process to roll the RC firmware back is pretty much the same as that for the main aircraft:
- Make sure Assistant can see it
- Close Assistant and open DUMLdore
- Take a backup of the current RC firmware
- Copy the new (well, old I guess) .700 RC firmware to the controller - do NOT copy the aircraft ‘bin’ files by mistake, you must use the RC firmware
- The screen on RC changes to say “UPGRADING”
- The RC will reboot itself within a couple of minutes
At this point, I thought I was done as the controller reverted to it’s usual “CONNECTING…” display.
So I opened Assistant and it said 72% done - but the remote said connecting 
Cue mild panic… had I successfully rolled back my bird and four batteries, then killed my controller?!
After a minute or two of worrying and debating my options, the Assistant suddenly jumped from 72% to 100% in the blink of an eye and said Update Complete!
Assistant then showed that the remote controller was indeed now on v01.03.0700 