The hotzone drifts at random inside the control zone until someone forces it. There are two ways to do that.
Towers: climb one, clear it, find the ops room (usually one floor above your entry) and hold F on the main console until the bar fills. You get one digit of a master code. Post it in team chat immediately. When your team holds every digit, enter the full code at a keypad on a tower you control and the hotzone moves to that tower.
Drill Rig: build one at your FOB and feed it fuel from the FOB's supplies. When active it pulls the hotzone to itself, which costs a lot but needs no towers. Fortify first and activate second, because the enemy comes to you.
Tower counts vary by map and by match, so check the map every game.