After you boot your H2O and select language, connect the H2O to PC and sideload the FW.
To avoid upgrade to 3.19.xxxx you need to
patch the firmware , connect again the H2O to PC, copy the "KoboRoot.tgz" to .kobo, you need to enable
`Block WiFi firmware upgrade`.
To sideload 3.18.0 FW, download the firmware from
here, and follow the
Installation Instructions for Direct Zip Files.
Don't do anything till it finish.
EDIT: after you patch the firmware connect to internet and register, it check for update and say "you'r device is up to date...".