Until yesterday’s update to iTunes 12.2.2, you were unable to tell Apple Music that you didn’t like a For You recommendation. You could do this on iOS devices, but not in the iTunes app on the desktop.
You can now tell Apple what you don’t like. To do this, click the … button next to any song, album, or playlist, and choose Recommend Less Like This.
Apple Music will take this into account when recommending music in For You. It’s a good idea to do this whenever you see something you really don’t like, just as it’s important to click the heart button to tell Apple Music what you do like. You’ll get better recommendations over time.