okidata mb472 printer

I'm using Sierra and would like the printer to automatically print mix sized documents - the printer was previously setup on a Windows system and would print letter and legal size mixed automatically. I contacted Oki but the tech guy wasn't familiar with iMac and couldn't find anything in their manual that would explain how to set it up to switch back and forth. I've tried every variation possible and there doesn't seem to be a way to specify that the MP tray is for legal and the regular tray is letter.