First you need to suscribe to the module, once you are suscribed you need to select the module you want to use.

To enable de module open your steam folder:
.steam/steam/steamapps/common/MountBlade\ Warband/

and inside it run the script:
mbw_config.sh

select the correct module, save and quit.

now you can open Warband to play with the module enabled.