mic left and mic right to single TRRS mic
You can leave RING2 unconnected or you can connect it to sleeve. The second option means it will work on both three or four-wire cables.

3-pin            4-pin
Tip ------------ Tip
Ring ----------- Ring1
              +- Ring2
Sleeve -------+- Sleeve


By the way, the figure does not show RING2 as the mic connection.