In the FSM, it is called the Aero Shield, and it is held in place by 4 bolts, 4 trim pins, and 2 push pins. To install, tighten to 10 Nm (89 lb-in). Likely find it in Emissions Components along with the Vapor Canister.
Might be these two, but I can't tell 4 sure: FORD OEM Exterior-Air Deflector Left BT4Z7811398B FORD OEM Exterior-Air Deflector Right BT4Z7811398A