Tascam US-122L not recognized

I have a USB sound card/mixer of the type TASCAM US-122L.
I plug it in and start Audacity.
Then it is not listed in the Audacity drop-down menu where to choose the sound source.
How do I make it work?

/ Hans Gatu

That is not how it works. Please see Matrix:Module-usb-us122l - AlsaProject