Perhaps these instructions will help:
https://www.mobileread.com/forums/sho...d.php?t=226456
First you should have Linux set so that you can see "hidden" files/folders. The "Root" for this process is the "KOBOeReader" directory that you are in when you first connect using your USB cable. There will be the hidden folders .adobe-digital-editions and .kobo in that directory.
You should think of the install process as two separate installs, first adding the PNG file to your Kobo and having the Kobo software process the Image adding it to its database and home page. Then installing the software that will be launched using that image file. It is critical that the image file function normally, as an image that your Kobo displays before reconnecting the USB cable to install the rest of the program.
Luck;
Ken