To be able to remove the PCB from the case, you will need to disconnect the flat-flex cable that goes to the keys located at the front side of the device.

For this step you will need a spudger or a pair of nonconducting pliers, to push off or to pull down the connector from the pin header.

This step requires some force to remove the connector from the pin header, but be careful not to tear apart or rip off the connector from the flat-flex cable.

If you decide to use a pair of pliers for this step, make sure it is made out of plastic or some other non-conducting material, because it will touch the PCB and it could create a short-circuit.