Click on a clip in an audio track and it will open in the preview window.
You can then drag the blue horizontal line downwards, to decrease volume. Click any point in the line and drag down or up, to create keyframes.
The blue line on the audio track will echo the results, so you can see where the audio dips vs. narration.
You might also test the HIGH PASS audio effect, which may screen out some undesirable lower frequency notes.