Where are the Manual Overrides?

The manual override controls are upstairs in Orion Hall by the students you aided in combat. If you haven't done so yet, you first need to deactivate the Cerberus camera control. The camera control is on a bench near where the Atlas mech pushed through earlier.

The best way to see what I'm referring to is to check the IGN video walkthrough at about mark 22:03. I've linked that specific section in the previous URL. If you need the camera override, just rewind a few seconds.

Door override:

Camera control (ignore this image if the camera control has already been accessed):

It should be marked on your map. If not:

Now, go upstairs and in the central room, get the Datapad, near the window, then the Assault Rifle Precision Scope near the monitors next to the panel you have to use to override the door. Go down and force the door below the central room.

Source: http://vgfaq.com/walkthroughs/mass-effect-3-grissom-academy-investigation-side-mission-walkthrough/