Anyone familiar with removing/replacing volume knob on Sony STR-DH190 - DH590 line of receivers?

[JimBanville]

So I picked up this DH190 receiver for practically nothing. I’ve only tested by using its bluetooth capability with my iPhone and it worked great! Anyway, I was cleaning it up and discovered unlike every other knob on a receiver I’ve ever pulled off to clean (the receiver was filthy), you’re supposed to use a screwdriver stuck through a hole from inside the chassis to release it. I’ve seen knobs with set screws but nothing like this. Anyway, not knowing any better, I forced the knob off by pulling it and the white ring separated from the black knob itself. So I found the service manual for the similar DH590 model they showed how I should have removed the knob. Problem is putting it back on. Can someone look at this pic from the manual and explain what they’re trying to get across from the “ok” and “ng” drawing showing the orientation of the knob? And is there a certain way this white inner ring is supposed to fit on the knob? And what purpose does it serve? Thanks!