The plastic cover should be lose now and you should be able to pull it back to reveal the circuit board inside.

Unscrew the screw on the bottom right-hand side of the headphone using the #000 Phillips Screwdriver.

Finally, use your thumb to gently pull back the tab at the upper right-hand corner of the headphone and simultaneously pull the circuit board out.

The scroll wheel may fly out when you pop the circuit board out.