Ouch Tony!
Your first prediction is correct - it’s the big hammer!
I just went thru it this weekend for the first time.
Here is the post I followed and it worked fine:
How to reflash the operating system on the Onefinity BB controller (Full SD card image)
The first laptop I used - the SD card reader didn’t work, I didn’t know it - that slowed me down. Once I got a laptop that worked - it went fine - just takes time.
Once I get everything setup the way I want it I will take the SD card out and make a backup using this post:
How To Backup the Onefinity Micro SD Card
That will get me backup and running faster.