It's not that easy, I am afraid.... Do you have any Linux knowledge? Do you know about tools like mount, dd, mkfs, fdisk, etc.?
I would try something like a manual factory reset on your reader first. That is formating the reader and the data partition as described here:
https://wiki.mobileread.com/wiki/PRST...#Factory_Reset
It can be done via recovery shell or via usb access to the flash memory.