Remove the adhesive from the mainboard

Do not remove it entirely - it's a part of the cable

Slide the cable towards the mainboard by holding it as near the connector as possible

Do not pull by the middle or other end of the cable

If cable seems hard to remove, try to push one side of the connector using a pair of tweezers by spots marked on third image

Do not push center part of the connector as it can be easily bent

Repeat the steps for another end of the cable connected to the mainboard