Alas I have a Vivaldi and use a transport. I don't have the upsampler with the internet interface, so I don't use the Mosaic app.
But it looks like in the Mosaic app you would use the SERVICES button to select the radio.
You can ask over on the dCS Audio community forum. Some of the dCS employees monitor for questions.
Or, just sit down with the Mosaic app and select SERVICES then radio.