Insert the plastic opening tool between the frame and the rear case behind the first clip.

Rock the tool sideways, to spread the gap behind the clip and separate it from the rear case.

Initially this may not free the clip , but by repeating the procedure for each clip, it will begin to loosen the piece.

Repeat the procedure with the next two clips on that side

You may have to go back and forth between the clips to free all of them. Be patient, as the plastic frame is quite fragile.