Try removing the cover and the surround of the fuel filler area. I removed the license plate stuff, and then the filler, and then the inner tailite stuff before I could get at the outer lens. When you do get to it replace all the bulbs just because it's such a PITA to do. I'm sure there are others here who can give you specific help.
Another suggestion: If you can see the item, but can't get your hand in there - I had that happen when I needed to replace the power antenna assembly, I could see but couldn't reach it, so I enlisted the help of my neighbors young son who had long skinny arms. His hands and my directions worked out well. I gave him $50 for the two hours it took us both. The garage wanted to remove the rear bumper and would have cost me $250 +.