https://www.cnet.com/news/boeing-completes-test-flights-for-737-max-software-fix/

During the next-step certification flight, Federal Aviation Administration crews will join Boeing pilots in the air to evaluate the new MCAS software and determine whether it addresses problems around the nose of the aircraft being forced down during flight.

FAA certification is necessary for the 737 Max to fly passengers again, and there's no telling how long that could take. The agency itself is under scrutiny for a cosy relationship with Boeing when the Max was originally certified. So the FAA has extra hurdles to leap before it can satisfy airlines and governments outside the United States that the plane is safe.