Microsoft has pushed out a new update for the Windows Insider app, taking it to version 18.104.22.168.
The update appears to be the final step in deprecated the app, after the Windows Insider feature moved to the Settings in Windows 10 Mobile Redstone.
Now, when you open the app, you are presented with a link to the settings, where you can select your Ring.
It is not clear how the app works on devices which are still on TH2 at present.
You can find the Windows Insider app in the Windows Store here.