You first begin your search around the water around the Noisy Marsh. After searching the watery area, head into the marsh. Navigate you way around to the B-1/C-1 area. You'll encounter a text box stating that you hear a scream on the other side (not someone saying hello). Have your party traverse the area to C-1, 1-5. There you'll find the collapsed body of a soldier. He'll tell you that he wasn't paying attention while flying and fell of the ship into the dungeon. Your medic will then treat him, and you can make your way back to the bar to complete the mission.