In LibreELEC all config files are in /storage/.config
Copy /etc/lirc/lirc_options.conf to /storage/.config and change the driver and device lines
Then create a file /storage/.config/lircd.conf with the remote key config (the stuff that's stored in RM-850.lircd.conf in the tutorial).
Then reboot and hopefully it'll work.
If something went wrong (eg wrong device name - not sure where that hw:551 in the tutorial comes from) check with systemctl status lircd (or journalctl -u lircd) for errors.
Change the files, then restart lircd with systemctl restart lircd, look for errors again.
If no errors show up you can check the button/key mapping with irw /run/lirc/lircd.socket
If that looks fine, reboot and the remote should work in kodi too
so long,
Hias