Recording drum covers

New to recording world. Using Audacity to record drum covers with electronic drums and original audio recordings through a mixer. Within Audacity is there a way to adjust (lower) the electronic drum volume. Basically can you separate and edit drum track and original song audio track.

Any advice would be greatly appreciated.

Is that a USB mixer?

There are several ways to listen to a backing track while recording a new track, and then you can mix (and adjust the relative levels) later.
[u]Tutorial - Recording Multi-track Overdubs[/u]

If your mixer is USB and it can work as a playback device as well as a recording device it will probably work.

Or if you have open (“hear through”) headphones you can listen to the backing-track from your computer speakers with your headphones plugged into the drums or mixer.