In the most common case the assigned device is the USB controller to which your USB audio card will be connected.
### Fedora VMs
In a terminal of the template from which you user VM depends, install pavucontrol with:
~~~
sudo dnf install pavucontrol
~~~
Close the template and start or restart your user VM, insert your external audio device, open a terminal and prepare pulseaudio to use it with:
~~~
sudo chmod a+rw /dev/snd/*
pactl load-module module-udev-detect
~~~
Start the audio application that is going to use the external audio device.
Launch pavucontrol, for example using "run command in VM" of Qubes Manager and select your external audio card in pavucontrol.
You need to do that only the first time you use a new external audio device, then pulse audio will remember your selection.
If you detach your external audio device, then want to insert it again (or want to change it with another one), you need to repeat the previous commands in terminal adding another line at the beginning: