I am using Audacity 2.30 on Win 10. I want to express my appreciation for the audacity team. My wife is the music director for a small church and as such I am the default sound tech. Earlier today my wife (on piano) and a young girl (on vocals) flawlessly executed a song and it sounded great at the performance. They asked me to record it for the girl as she wanted to give it to her grandma as a Christmas present. I recorded it didn’t notice until after the fact that the left/right balance on the CD burner was off so now the vocals are fairly high and the piano is really quiet. Any tips on what I can try to clean it up?
If anyone wishes to hear the song here is the link >> https://drive.google.com/file/d/1ip5VlY6CezRYO8a_QlE91o1rYuIkpX_A/view?usp=sharing
If the piano is more on one side than the other, pan
towards that side & make a mono-mix.
[ Could than make a pseudo-stereo version of that mono-mix ].
If you click the drop-down arrow in that same little window and select Split Stereo Track you’ll be able to adjust/edit the left & right channels independently.
…And this is up to you, but it will probably sound more natural with the vocal and piano both panned to the center, or near the center, rather than having the piano coming out of one speaker and the vocal out the other. Or, you could mix both channels to mono. (A true-mono recording will play through both speakers.)
That is basically what I did but unfortunately both channels were identical so my effectiveness was limited. The final result was still soft but not as bad as the original
https://drive.google.com/file/d/1ME60s9PSdFfsgrlPct-jia_3fnDEpup7/view?usp=sharing
Their voice only goes down to ~350Hz , the piano goes down to ~50Hz,
so by boosting the bass you can selectively make the piano louder.
Wow! That sounds amazing! What bass settings did you use if you dont mind my asking? I cant seem to replicate what you did
I am not trying to get you to do it btw, I am still learning audacity and how to be a good sound guy 
Okay I think I got it, better at least. Thank you for your help @Trebor
https://drive.google.com/open?id=1SNqEFD2bixL99BPFu-x9SMDyctF7KTpq
Boosted everything below 350Hz, only the piano lives there.
Boosting the bass does make it a bit muddy, but it does make the piano louder without affecting the voice.
Compression raises the volume of all the piano frequencies, not just the bass.
If you get a (free) real-time equalizer plugin for Audacity you can quickly learn by trial & error, e.g. …
(NB: Currently only 32-bit plugins work in Audacity, even if your machine is 64-bit).