Ah, I see part 13 now.. but not sure how to get it because that whole grab handle seems stuck pretty good.. I'm afraid to break something.
After looking at mine, there is no little cover for the bolt. The entire grab handle is one piece and the window control all together in one piece. Not sure if once you remove this little panel with window switch if it would expose the bolt. But then again not sure if the bolt is holding anything to the panel door.
Here is a pic. I will have to remove it myself to find out the real deal on this or ask someone here that has swap out there back speakers themselves.
One of these days I will make a video on removing the rear panel.
If you lost a bit, my suggestion is to tape it to the screwdriver just in case it doesn't fall again.