You can register your device either through the AirVisual app or website.
First, you need to create an AirVisual profile. You can do this from the IQAir website by clicking the 'Sign In' tab at top right, then 'Create an account' using either a Facebook account or email address.
Once registered and signed in, you can select 'My devices' and then 'Add a device'(see image below) - this will register your Pro to your account.
Using the AirVisual air quality app, just select the '+' menu button, choose 'Manage my devices & Wi-Fi', and follow the steps.
Using the APP: