Lift the brown holding tab up on the connector (Image 1 orange arrows)

The ribbon only has writing on one side, that side needs to face towards the clear plastic sensor on the other end of the board

Feed it into the connector and while holding it in place with your finger and thumb in the centre of the ribbon cable, push each side of the brown connector tab down until the connector grips the ribbon cable

You should notice the tops of the metallic strips/pins stuck out the top of the connector should be uniform (Image 2). If you have put it in incorrectly, then there will be more of the strips/pins showing at one end or the strips will not be visible because it is in backwards