Do it from the Source Monitor or (I think) Project Panel; it won't work from the Program Monitor or Timeline Panel.
Still doesn't work...
Import the .r3d. In the Project panel, choose Clip > Source Settings, or right-click (Ctrl-click Mac OS) and choose > Source Settings.
Working here for me.
In your screenshot, it appears you want to adjust the Source Settings for a clip in the Timeline. You can't do that.
You have to adjust Source Settings for a clip before editing it to the Timeline, not after.
Hope that helps you.
IT WORKS!! Thanks so much