Take the KoboRoot.tgz of the folder KoboRoot_3.3.1_3.4.1 of the archive KBStartMenu_04_update01a.zip, which you can find
here. In the menu select "handle update" > "install_update". After the reader has rebooted into nickel, connect to the pc and delete the folder kbmenupngs and the folder kbmenu of .kobo.