How do I unregister Orbi from remote management on Orbi app

I just setup an RBK50 system for my brother (I have the same system already). I used the existing remote app on my phone to test it, enabled remote access and now I show both mine and his system in my remote app. He installed the app on his phone and can access locally but when trying to access it remotely, he gets the "This NETGEAR device is already registered with another account" message. How do I get it unregistered from my app so that he can add it to his?  Thanks.