Use a spudger to flip up the black plastic tab holding the remaining ribbon cable in place. The black will rotate up 90 degrees, releasing the ribbon cable.

The tab is very fragile, so be careful when flipping it up to unlock the cable and down to lock the cable.

The plastic tab may be white (instead of black) on some iPhone models.

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