The Restore/Add function allows you to restore previous purchases onto a new device, or if you have made a Artscroll.com purchase, you can link your device to your account here.
To restore previously purchased content to the device on which it was purchased, please see: My Purchased Volumes
To restore Apple purchases to another Apple device using the same Apple ID, please see: How can I access my Apple purchases on another Apple device?
To restore Apple purchases to an Android device, please see: How can I access my Apple purchases on my Android device?
To restore Android purchases to an Apple device, please see: How can I access my Android purchases on my Apple device?
To restore Android purchases to another Android device using the same Google Play account, please see: My Purchased Volumes