The folding mirror button is located right next to the heated mirror button, above the mirror adjustment toggle. Maybe only available as an option?

I guess I could take out the glass to see if there is a heat element built into the back of the glass, but I'm paranoid that I'll break something since I don't really know how the assembly is constructed. I don't want to have to replace the whole thing if it breaks (big $, even used). I might just take it to a glass shop and have them take out the old glass to inspect, then either order the regular glass from them or the heated glass from the dealer and have them install it.