Take the small phillips screws and hold it steady while screwing them in around the perimeter. You'll need to drill pilot holes so screw just enough to make a mark as a guide. I used a 1.51mm bit.
The drilling will create a lot of plastic debris, so it is best to do this before mounting more components inside.
Repeat this for the other side. Do not attach the panels yet.
Make sure the holes line up and move on to the next step!