Warning! Lift out the optical cable from the clear plastic sensor on the back of the circuit board (top right) before attempting to move the board (Image 1)

The circuit board should slide forward and up past the grey sprung catch (Image 1) to reveal the back of the board and the socket without it's ribbon (Image 2 pink arrow)

Now its time to get the ribbon cable in side the housing (Image 2 orange arrow). Look on the left of the housing and find the vertical slot. (Image 3)

Feed the ribbon cable in with the metallic strips/pins facing away from you

If you succeeded you should see the metallic strips/pins facing you when the ribbon naturally flexes (Image 2)