The Smart Vent Identification Mode toggle is located in the Home Settings -> Flair Devices tab. When enabled the light bar on Smart Vents will display a unique pattern that identifies the Smart Vent.
It may take a minute or so for the light bar on the vent to turn on or off after enabling/disabling this mode. Please note there is a timer that will toggle off Smart Vent Identification Mode after 30 minutes if you have not done so already.