On the bottom of the P16-HQ, use a #2 Philips Screwdriver to remove all ten screws

The four longer screws go on the left and right edges

The shorter screws go on the top and bottom edge and the mid-plane which hold the internal PCB so they must be removed before you try to remove the bottom plate

If the plate is still firm use a spudger to pry it off - the top edge was the easiest for me.

Note: There are three additional screw holes for a mounting plate but they're not used otherwise