You are pressing the center of the wheel, on the Flying M, right?
It's behind the right side Fog Light/Blank. To access it you have to remove the small cover underneath the corner. 2 philips screws in the little air dam in front of the tire, accessed from the wheel well, 3 philips/10mm bolts underneath around the outer edge, and 2 plastic retainers on the inside edges (pry the center piece 1/4" out to remove the retainers).
Once that piece is off, you can reach up and unclip the Fog Light Blank by pinching the tabs starting at the end towards the center of the car. The outside tabs are slip fit and pull out horizontally.. If you have the Fog Lights, removing it is more complicated. You should be able to reach the horn without removing the Fog Light.
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