the easiest way for me to do this is to demux the audio from the video file (VD in direct stream mode), then use a multi-track audio editing app like Audacity, CEP, Goldwave, etc, and use the video audio as the guide for your secondary audio. For me it's easier using an audio app since they do a better job of zooming in on the audio file so you can see the peaks and "beat" so it's easier to sync up. Just pick a place at the start of the video audio, and find the same spot on the second audio. Then just select the same start and end point as your video audio on the secondary audio, and export/save to a new file. Then just place back in your timeline (or remux with the original video with VD using Direct Stream Copy choosing wav audio).