In the future, please respond to the other post regarding this subject. Creating more than one post on the same subject is quite annoying.
To answer your question. Go to the free roaming camera. Click on the opposite end of the train and you are now in the other cab. There is a driver command or session rule, but I can't remember the name for it. I could never get that to work though because I think it was meant for a single-car EMU or DMU, and not a full train.
John