System UI Tuner

System UI Tuner

I have a Nexus 5x running Android 7.1.2 beta 2. I've been trying to access the System UI Tuner. I follow these instructions:
"Pull down the notification shade on your phone, then open your Quick Settings menu."

"Tap and hold on the gear icon at the top of the screen for about five seconds."

All is fine up to this point. I pull down the notification shade. It says no notifications. I long press on the settings gear wheel for five seconds, ten seconds, and either nothing happens or I go to the settings menu.

"You’ll then see a message that says System UI Tuner has been added to Settings."

I don't see any such message.

"Open the Settings app on your phone and scroll to the bottom. There you’ll find System UI Tuner."

The bottom of my settings screen is still "About phone".

Am I doing something wrong?