Get a good head light to view this tiny Jumper burried deep inside the tangled web of criss-crossing SATA cables and Power cables in that very congested neighborhood with the motherboard already anchored to the pan and all the devices like your Multiple HDDS jutting into the tiny space and the front panel cables ready to get off their pins with any forceful separation of the obstructing cables to get to the target.
Attached is a bird's eye view of your System board with the target marked. Good luck. It is a tough job after the build to go back into the Computer's belly to do any type of exploration. Before getting off the casse and closing the cover, please make sure you haven't knocked any of the RAMs from their sockets or pulled the Front Panel wires off especially the PWR switch cable, one of the most common causes of "Failure to Boot "or "Failure to Power ON" on a newly built system!