Adjust any track with its fader on the left of the stem, or ask Nova. How Nova balances a mix depends on the full context of your tracks.
You can adjust the level of any individual track in two ways:
When you ask to bring up one element, like the vocals, Nova's approach depends on the context of your full mix. Sometimes raising the target track directly is the right move. Other times, creating space by adjusting the surrounding tracks gets a cleaner, more balanced result.
If you want a specific track changed and nothing else touched, use the manual fader on that stem. It gives you direct, precise control over that one track.