Pull out head unit, display and cubby Aux is in. Personally, I would wait until you have everything, rather than doing this twice. It is one of the more challenging parts of the install. If you have any Romex house wire in the garage that too works well for fishing cable through tight spots.
From my article:
"Install new USB/Aux harness: You will have to remove the green connector from the large block connector, from front of connector there is a small keep that needs to be actuated and then connector will slide out. The Media In harness which is the yellow 4 pin connector and green connector is tied to the larger harness. Therefore, rather than remove I just put the new cable in, you can tie the old connectors to cable with tape so they will not rattle. The new harness is difficult to fish from the cubby to the infotainment. I removed the side panel and took a bicycle cable shroud, these work great for fishing cabling. If you don’t have one just go to your local bicycle ship and ask for one they have replaced. House wiring cable is also decent, a clothes hanger is likely not long enough. After removing side panel I started from there and went half way through dash, reached up and pulled down to cubby. Now I could tape USB/Aux yellow and green connectors to my shroud and fish up harness to infotainment unit. Green connector will slide into large connector."