Firstly, the pilots know about runaway stabilizer trim - there is training and/or written procedures.
They did not now about MCAS, when the stabilizer was doing unexpected things some pilots mis-diagnosed the situation.
On the flight prior to the fatal Lion Air one a pilot in the jump seat diagnosed what was happening though did not now why, so advised the flying pilot to turn off the stabilizer trim. Sadly, on the next flight poor crew coordination in switching roles left the F/O confused and not taking the correct approach.
The pilots of the fatal Ethiopian flight knew of MCAS but somehow got confused and/or simply ran out of time (the airplane was moving fast and close to the ground, out of that hot and high airport).