You should now just have the PCB attached to the bottom housing.

There are two clips shown in the second photo that hold the PCB to the bottom housing

Use your fingernails or something similar to pry the clips away from the PCB.

After this step, the mouse wheel should detach from the PCB on its own.

The PCB may still be attached to the housing from the battery coil wires. Carefully remove them from the housing.