Kobo Touch N905 - need external sd boot

Hi,

I bricked my Kobo Touch n905 (not the one with internal sd-card)

bricking was succesfuy done by installing xcsoar and changing usb-otg settings in the xcsoar menue (xcsoar is a great , in my opinion the best soaring navigation software and the kobo touch n905 (a) works with it as long as usb-otg setting is not changed).

before bricking i made a backup.img
now the blue light is blinking, by pressing the home button when sliding the powerbutton the led lights constant blue. when i press the reset button home button and powerbutton in all possibe combinations, blue light changes to red light.

i want to made the kobo boot from an external sdcard by holding the home button when sliding the power button.
when some system is working i can write the backup.img on the internal memory via usb cable.
i dont knwo how to make the sd card with some linux distribution.
according to a thread in this forum (link below) i have to make a partition on the sd card with ext2 filesystem and then copy (?) debian there..
can someone give me a hint how to start?
https://www.mobileread.com/forums/sh...d.php?t=289206