You just need to remove the same large phillips head screws you would remove to examine the blower motor itself. The large plastic intake grille is where the flap is, on the underside.
You can remove the colored plastic vacuum lines on the right side first, i use a 6mm open end wrench to lever them off of the vacuum servo. You want to see if the rods inside the cover is actually attached to the flap.
If you've never taken this cover off before, there are I belive 2 out in the middle of the cover, one on the far left and I belive 3 on the far right perimeter, really have to look for them though, especially the front and rear ones on the right side.