They did two things for two phases of the satellites' lifetimes. In the first phase the satellites are raising their orbits to their final position over a period of a month or two, and SpaceX started rotating the solar panels to reflect less light toward the Earth. But they can still be visible sometimes, until they reach the operational phase when they are in their final, higher orbit.

For the operational phase SpaceX added a sunshade which reflects light away from the Earth. This plus the higher orbit makes the satellites dim enough that they cannot be seen with the naked eye. This sunshade was designed with feedback from astronomers at the often mentioned LSST, which is the single telescope most affected by large satellite constellations. It will prevent artifacts from the imaging sensor's pixels becoming saturated, which is the main concern. The satellites will be visible to the telescope but can be filtered out with standard techniques already in use to filter out the thousands of other satellites already in orbit. See https://www.spacex.com/updates/starlink-update-04-28-2020/

The satellites were only human eye visible because SpaceX let them tumble for a while right after launch. They changed operations and now they're no longer visible to the human eye (generally).

See here: https://www.spacex.com/updates/starlink-update-04-28-2020/