load an image and open the tone curve panel (you already did this probably). at the lower right of the canvas you'll see a button with "!" on it. click the button to convert to "2012 process". wait. when it is done if you *still* don't see the channel dropdown click the "edit tone curve" button to hide the sliders and *then* you should see the channel dropdown.
I found this totally mystifying, but once I found it (luck) I get it...new features, new entries in the database or some other magic. anyway the video sure didn't give me a hint.
this will be my 5th try posting an answer to your question, hopefully this time it will work, no thanks to support, 5 times resetting the password, etc etc.
