Once you gain control, you'll see two Elites head down a ramp in front of you. Follow them down to find the rest of the Lance. As one of the Elites works at a locked door hand off your plasma rifle to one of the grunts. He'll be far more effective with it. This said, you may find it more efficient (depending on difficulty level) to take out the Grunts while your Special Ops team fights the lance coming via elevator while flanking them for an attack from the rear. There are two banshees waiting. Choose wisely.