Install

An ebook reader application supporting PDF, DjVu, EPUB, FB2 and many more formats, running on Cervantes, Kindle, Kobo, PocketBook and Android devices

In other words, KOReader can replace the default firmware of your eReader.

Steps for Kobo (automatic)

You have to check documentation and refer to this guide.

Power on eReader
Connect USB cable
Allow share (if KOReader is installed) or connect if native kobo is installed
Go to https://www.mobileread.com/forums/showthread.php?t=314220
First post
- Download KOReader | OCP-KOReader-vX.X.zip at the end of the post
- Create folder on your disk, and put archive in it
Second post
- Linux: Download the Linux install script archive, and unzip it in the same folder. Run the install.sh script with your favorite terminal emulator.
- macOS: Download the macOS install script archive, and unzip it in the same folder. Run the install.command script (Right Click > Open > Then click Open in the GateKeeper popup)
- Windows: Download the Windows install script, in the same folder. On recent Windows versions (i.e., when running PowerShell >= 7), you'll have to "unblock" the script to allow it to run. (Right Click > Tick Unblock in the bottom-right corner).

- Downloads
  - koreader
    - OCP-KOReader-vX.X.zip
    - install.sh / install.command / install.ps1

Check file .kobo/Kobo/Kobo eReader.conf on your Kobo device.

[FeatureSettings]
ExcludeSyncFolders=(\\.(?!kobo|adobe).+|([^.][^/]*/)+\\..+)

In case you skipped it, read the note at the top of the page, as you'll most likely have to prevent Nickel from scanning our custom directories as part of the installation process.
Download the latest install package for KFMon.

- Downloads
  - kfmon-X.X.zip

Extract the full content of this archive into the root directory of your device (i.e., not under any subdirectory).
Download the latest release of KOReader.
Extract the koreader folder of the zip into the .adds directory of your device (a directory which may have just been created by KFMon's archive).
Eject & unplug your device. Nickel should then appear to be processing a book, before restarting to process an update.