Insert a Jimmy into the gap between the front and back cover assembly at the bottom edge of the Stadia controller right to the headphone jack.

Tilt the Jimmy upwards and push it into the gap between the covers at the same time to pry open the plastic clamp.

Repeat the previous procedure at the clamp left to the headphone jack.

Do not try to remove the front cover assembly all the way yet. It's still connected to the rear cover assembly.