Ok there are numerous ways to go about having music in your game. My chosen method here will be to just have an empty object. This is super easy and will let you create the music to stay the entire game.
Once you have that setup all you need to do is drag your audio onto the AudioClip portion of the Audio Source component. Given this is background music we will also want it to loop.
You can adjust settings on the fly as you test to see where you would like your levels to be at. You can even manipulate these settings in a script but that’s a bit more advanced than this article is meant for. Given Medium doesn’t like to accept video I am linking to my youtube page where I have the demonstration of this step setup. Haven’t tried this before so if it doesn’t work for you let me know please and thank you.