They just press on the shaft . All you need to do is pry them off, I sometimes use needle nose pliers. Shouldn't be on there so tight as to damage them.
I have taken a number of these panels apart and can say that the knobs (inside steel retainer) can seize onto the aluminum shafts. When that happens, I use Blaster PB on the shafts and let it roll down into the knobs. Let the penetrating oil do its job and set the panel aside. See what happens in about four hours with only your fingers. If they don't come off, repeat the above. You will not need to pry them off.