Now that the passenger side cowl grill cover is removed you can open up the drivers side cover and clean under it or if you didn't really have any debris accumulation in the passenger side just put the cover back on.
To clean under the drivers side cover, you need the wiper arms to be close to the vertical position near the cowl grill cover to get the best access to clean under the cover without removing the wiper arms. Both wiper arm shafts go through the drivers side cover but you don't have to remove them to clean under it with a shop vac.
I would recommend placing a rag between the wipers arms and cover to protect the cover from scratches. The position of the wiper arms in the image below are about optimal to get access under the cover to clean the area with a thin shop vac hose.
When your done cleaning and ready to put the drivers side cover back in place. You want to look under the cover and get the clips and post lined up with the holes that are punched out in the sheet metal as pictured in the image below. The cover will snap back in place when you push down on it. (Don't Force It). After you have the cover in place check it from the windshield side of the hood and push down on the cover as needed so the cover is flush to the windshield.
When replacing the passenger side cover be careful not to damage the attached rubber seal that is on the end of the cover near the hood hinge. Again line up the protruding clips on the bottom of the cover with the holes in the sheet metal. The covers will snap in place when you push down on them if they are lined up properly. Make sure all the snaps are in and the cover is flush against the windshield.
On my Sable the second clip location from the passenger side fender must have been an after the fact addition and the plastic cover and the plastic base under the cover were not modified for the extra clip. Because of this the clip was barely grabbing onto the cover so I took a couple of minutes with my Dremel tool and cut a slot into the base.
This photo really didn't quite do justice to show the large amount of leaves and debris that were actually in the shop vac.
Now that I own the car I park near pine trees so I have pine needles blown into the vent and other openings in the car.