I have dirt/marks inside on my rear window where the 3rd brake light is. I have tried putting a towel in between the window and light but I can not get the window clean. I tried to look into removing the rear window speaker panel but, I am not sure what to do.

I use one of the little Swiffer 360 Duster clothes to get behind there.. Just use it without the wand and slide it in/out a few times and it seems to do the trick,

Removing the rear panel is a pain to do