Can anyone explain how to do this? It feels stuck and I dont wamt to force it?

From the inside of the helmet you’ll see a catch on the front of the mount and corresponding knob on the underside of the plate. You need to get your finger under the front edge of the catch and pull it downwards. At the same time give the plate a robust push from above at the back. The catch is pretty strong / stiff and mine needs a bit of effort to deflect sufficiently.

Good luck!