Installation,
extract the mod file with replacement.
Example:
D:\SteamLibrary\steamapps\common\Mount & Blade II Bannerlord\Modules\SandBoxCore\ModuleData

You will also need mods:

For Gondor
https://www.nexusmods.com/mountandblade2bannerlord/mods/5000

For Isengard
https://www.nexusmods.com/mountandblade2bannerlord/mods/5037