PDR (Paintless Dent Removal) is a process for fixing dents on the metal skin of your car, not the plastic bumpers. If you want it perfect (dents removed, and perfect color blend etc.) take it to a professional body shop, but if you're fine with it looking ~85%, I would first lightly sand the areas where the scratches are so that the plastic is smooth again, and with a find brush apply the touch up paint (make sure it's mixed with clear), then wet sand it so it's flush with the original paint, and polish. This is a rather simplified version of the process but there are some great YouTube videos that delve into more detail. I'll link a couple for you.
I used these two videos to touchup my driver's side door as I had some chips on both the metal itself and a large chip on the plastic near the key hole, and now you have to put your eye within a few inches of it to notice. Also make sure you get actual touchup paint, I used left over paint for the spray gun supplied to me by the shop who repainted my bumpers and trunk, and its much more liquidy (so it sprays evenly through a paint gun) and isn't well suited to touch up (I was limited to small-medium sized chips) So just beware of that.
Hope that helps, good luck
Bookmarks