Hi,
You need to set the Action targets to subscribers that are subscribed to list A and set an action to unsubscribe them from list B and C.
I'm not sure how you want to filter your subscribers. In case someone is subscribed to three lists on which list should you keep the subscriber?
In case you need the subscriber on only one list in order to prevent sending the same email twice to a subscriber then there's no need to worry. By default Acymailing will an email only once to each subscriber, even if they are subscribed to several lists. If you try to send the same email a second time, Acymailing will ask you if it has to send the mail to all subscribers (including the ones that already received that email) or only to new subscribers (those that have not received that email before).