It looks like Microsoft have made a total mess of this.
Try this, but ensure that all other programs are closed before you start (my computer crashed on one of my attempts, even though this is a clean and fully updated Windows 10 testing machine - there appear to be system level bugs here).
- Right click on the loudspeaker icon in the Taskbar and select “Open Sound Settings”
- Click on the link “Sound Control Panel”
- Close the “Sound Settings” window.
- In “Sound Control Panel”, select the “Recording” tab
- Ensure that the default device is set to any available device that is NOT the device that you want to change.
- Right click on the device that you want to change and select “Properties”
- Select the “Advanced” tab
- Select the Channels / sample rate that you require
- Click “OK”