I just moved to a new home with rachio 3, when I try to set it up in app it shows up “controller already in use” msg. How can I delete the previous owner controls and add myself?
Have you seen this article yet? Transfer ownership of a Rachio controller to your account
yea, but everytime after scan the barcode, it pop up the msg directly. 
Sounds like the first option will not work for you. You might have to do option 2 or 3.