My CH6 came with double-sided adhesive tape in between the board and the backplate. Some pressure and fiddling is needed to loosen the glue without damaging the board.
I got feedback on Reddit as well. And I guess that the backplate is held in place by sticky thermal pads. It was recommended using a hairdryer to help get it loose. If anyone have experience of using a hairdryer that way, feel free to chime in.
Just hold the hairdryer in the direction of the backplate to heat it up. 😛
Personally I cautiously poked a flat piece of plastic in between the board and backplate to loosen the adhesive pad. You can also push on the screwing pins that go through the mainboard holes.