I assume you're talking a Linux thing (which I am also new to) not something built into Rockbox. I'll have to find out how to do that for future reference.
I already solved it by brute force. I couldn't do a thing with it on the Linux box, so I hooked it up to my Windows computer, uninstalled Rockbox, formatted the thing, and reinstalled Rockbox. I did a small test, putting music from one CD on it and things seem okay again.