ORBI app that was controlling my old ORBI system won't reset to recognize my new ORBI system.

Greetings!  I have a new ORBI 852 mesh router system, to replace an RBK50 system that's slower.  The ORBI mobile app has been controlling the RBK50, and won't allow me to reset for the new ORBI 852.  I tried uninstalling the mobile app, then reinstalling it.  It still thinks I'm using the RBK50 router.  How can I get the mobile app to fortet the RBK50?