hi utra, maybe i can help you fix your kobo
1. you must disassemble your kobo, open back cover, let do it carefully
2. you can see micro sd card, then put it out and connect it with card-reader to computer
3. format micro sd with fat32 32kbp option, if done it's maybe use normal, if not, you can change a new micro sd card (8 / 16 / 32gb) then format it same as on.
4. use
win32diskimager then follow the picture
https://ibb.co/VCv3B5z
5. when micro sd card has written, put it in your kobo and wait several minutes
good luck!