The AI in battles (Total War: Warhammer)

How to transfer control of the army Intellectu in battle? In other parts you had the chance to choose who will run the second, the third army in the same battle, Vahe I can't find such button, to control himself with three armies is not always convenient, especially when against me meeting chaos, I would be that the AI is distracted the part of the troops, and I have already dealt with the rest, but the game gives you to control either 20 or 40 units+reinforcements and keep track of them all is not convenient, while one distracted, the other side has a full kick I basically don't put the fight on pause, like the motion, but 40+ units a gesture