Monitor Calibration.

I had the same question, but by going into ColorSync via System Prefs (instead of the ColorSync app) and pressing the option key (on a re-mapped PC keyboard) got into the advanced mode and got the job done. BTW, when I was done the new cal was so close to the old that I can't tell the diff!

This was for an Apple Cinema on a 4.1 upgraded to 5.1 tower, 10.13.6