Beyond the four EQ bands, this tool includes a master volume control that goes up to 150% for tracks that are recorded too quietly.
Push the master volume gradually and keep the built-in Limiter switched on — it catches sudden peaks so a big volume boost doesn't turn into harsh clipping. If a track still sounds distorted at high boost, the source recording itself is likely already clipped.
Raising the master volume increases everything equally, while boosting an EQ band only raises that one frequency range. If a track feels quiet specifically in the vocals or bass rather than overall, an EQ boost in that band is usually a better fix than a blanket volume increase.