They'll have to find some debris first. So far none of the satellite sightings have resulted in recovery of anything conclusively connected to the aircraft. If

They'll have to find some debris first. So far none of the satellite sightings have resulted in recovery of anything conclusively connected to the aircraft. If they do find debris they can then check the ocean current data for the time since the crash to extrapolate a rough area where the flight data recorder might be. Even then, it could take a very, very long time. Air France 447's FDR wasn't found for two years, and they knew where it had crashed within less than a day.