Go into the can gateway which is module 19, then into the 'installation list'
once in there you will see all available modules and the ones that are installed will have a tick next to them so just add a tick next to the trailer module (number 69) then save and exit
once in there you will see all available modules and the ones that are installed will have a tick next to them so just add a tick next to the trailer module (number 69) then save and exit