You can adjust the background music volume of your entire video either on the Storyboard screen or the Advanced Editing screen.
Follow these steps:
Step 1: On the left panel, go to the Music tab.
Step 2: Under the selected music track, you can adjust the volume to your liking.
Step 3: You can also click the green volume button to mute or unmute the music for your video.
If you have added a video clip or voice over in any of your scenes, you can adjust the background music volume for that scene against the volume of these elements.
The background music volume set in the left panel will always be the highest volume you can set throughout the video.