Insert the flat edge of a metal spudger in the seam between the adapter body and the plastic casing. Move the spudger into one of the corners.

Push down on the spudger to separate the casing from the adapter until you hear a click and the casing stays open on that side.

Do the same to the other side until the casing comes off.

When reassembling, first align the headphone jack in the back of the adapter body with the hole in the casing, then align the tabs on the floor of the casing with the holes in the bottom of the adapter body.