How To Select Rolling Stock Liveries?

Hi,
Does anyone know how to select the custom livery you want to use on your rolling stock?

 

If it is the train you are going to drive, Press x on Xbox, tab on pc, idk on ps

 

Sorry, I don't think that has worked.
I made a livery for the EWS JNA hoppers which makes then DB, but I don't know if it is possible to use these trailers in the timetable. I think I should have said 'Wagon' rather than 'Rolling stock', as obviously that includes locos too. My mistake

 

In that case, you can't. It selects wagon/coach liveries at random.