Ribbon cable "3" is held in place by a FPC style connector. You must unlock this connector before sliding the ribbon cable out. The locking mechanism is on the opposite side of where the cable is inserted - it swivels upwards 90 degrees. Use a plastic spudger to lift the locking mechanism.

The FPC locking latch is very delicate and is typically a different color than the body of the connector. (see the detail image of FPC connector open and closed)

Slide the ribbon cable out of the connector, and remove the display assembly from the iPhone.

It's impossible to properly reinsert a ribbon into an FPC connector unless the lock is disengaged. Make sure the locking latch is open when attaching/detaching the cable.