You can choose any of your Bersekers, wherever he is. If he moves, he will straighten. The personalities move at the current battlefield. There needn't be any units there for you to play this. All in all, it's very versatile card. If you have more questions, you can search for rulings on "Countermove", which is almost the same, except that the performing tactician has to be at home.
Bane of Salman Barakat * Red Shirt * The Dynasty: Greek Division