To rename your AirVisual device, you must be its owner and you must be logged in to the app or website with the email account that owns the monitor.
In the app, go to your device page and click on the settings wheel in the top right corner. In the setting page click on the Device info section and proceed to change the name. Allow for couple of minutes for the device to refresh with its new name.
On the IQAir website, log into your dashboard. Simply click on the device you'd like to change name, and in the device detail page, place your cursor onto the name of the device and key in the new name.
