Facing the back of the drone, remove two screws retaining te optical sensor unit.

The optical sensor is also retained by two clips underneath it. With both thumbs, push it up firmly from the bottom to release it. (In the photo, my other thumb was holding the camera.)

It's still connected by a ribbon cable. Take care not to strain it.

Turn the optical sensor over, in an upwards direction, and remove two screws to release the retaining clip.

With a spudger or similar tool, gently lidt a corner of the connector to disconnect it.