Firstly we need to stop Kodi and Lirc so SSH to your device and type the following commands

systemctl stop kodi
systemctl stop eventlircd

Next we need to scan for the IR codes

ir-keytable -t

Now press buttons on your remote and make a note of the keycodes in notepad

Now with the keycodes you need to create your map you can look at https://github.com/LibreELEC-AML/LibreELEC.tv/tree/master/packages/sysutils/v4l-utils/keymaps for an example and here https://github.com/tirithen/xbmc/blob/master/xbmc/platform/linux/input/LinuxInputDevices.cpp#L126 is a list of all available commands to map the buttons to

After finishing your file it must be saved in

/storage/.config/rc_keymaps/YOURMAPNAME

Next edit the following file

/storage/.config/rc_maps.cfg

and add the following line

meson-ir        *     YOURMAPNAME

Now load your new map with the following commands

ir-keytable -a /storage/.config/rc_maps.cfg -s rc0

Start Kodi and test your map works

systemctl start eventlircd
systemctl start kodi