Use the tip or the flat end of a nylon spudger to unlock the connector securing the flat cable of the keyboard to the logic board.

Pull the flat cable out not up.

When re-assembling, insert and hold the flat cable in place with one hand; use the other hand to lock the connecter using the tip or flat end of a nylon spudger. If you release the flat cable before locking the connector, it will most probably slip out.