Judging by the inforation in this thread:
https://www.mobileread.com/forums/sho...d.php?t=193411
You can fix it, if all else fails, by breaking it further.
The back of the device can be removed, and the firmware accessed directly by removing the factory installed sd card. You'll have to get a full backup copy of the firwmare from someone, and if you aren't sure how to restore an OS image like this, I woudl advise finding someone to help. (A local Linux Users Group would probably have the kinds of nerds you need.)
(Remember the days when Kobo made devices that would sensibly boot from Sd card?)