Could you clarify and/or verify what you want to do.
I am reading your question...
You have imported a file with video and audio components, and one audio component includes voice and soundtrack, and the soundtrack is overpowering the voice. In such a case, I see no way for you to separate and edit those audio streams in the audio portion of your file.
If details were other than the above....
You could right click the Timeline file and select Delete Audio, and then import a replacement audio file.
If you had video on Video Track, narration clip on Narration Track, and soundtrack on Soundtrack, you might try to use the Smart Mix feature of the program to balance the audio, one against the other. You could also look at the Audio mixer in this regard.
Please review and consider and then we can discuss this further.
Thanks A. T. Romano for the response. Your first suggestion won't work
because the voice audio would be very hard to get again. However I will try
your other suggestions and let you know if I have any success.
Thank you for considering the troubleshooting selections.
We will look forward to your results - as your schedule permits.