Hopefully one of the hardcore Kobo users who collect disk images will see your post soon. The Kobo Vox is ten years old. That takes us way back. I only used the Kobo iOS app on my iPad at that time.
I found some links for you in the meantime:
http://download.kobobooks.com/learnm...user_guide.pdf
I found this chat (
https://www.mobileread.com/forums/sh....php?p=2539812), but the disk image links are dead. It's an old thread.
However, this other thread is from 2011 when the Vox was new. Perhaps some of these tips will help you reset your device:
https://www.mobileread.com/forums/sh...d.php?t=162118