Honestly it's so easy I don't think it deserves a how-to.
Just remove the pop clips under the bottom and the two by the hole, remove the screws nearby, cut a big peice of screen mesh about 12 by 6 inch, mark where the holes go for the pop clips and cut the out with scissors, then pull back the fender liner and shove the screen in aligning the holes, put I one clip to keep it in place, tuck the fender liner back in behind the fender, install remain clips and screws.
So the screen is clamped between the fender liner and the plastic vent piece, and held in by the pop clips as well.
I guess if you want to get fancy, you'd take the liner out, clean it, and glue the mesh to the back of it with PL Premium, but I think it'll stay put and is easily removed or replaced this way.