There are a number of ways to adjust the volume of content in FMOD Studio.
You can adjust the volume of an audio asset in the playlist of a multi instrument by selecting the asset in the multi instrument playlist and then adjusting the playlist entry’s volume control in the deck.
You can adjust the volume of an instrument by selecting it in the event editor window and adjusting its volume control.
You can adjust the volume of an event by selecting it in the events browser and adjusting its master track’s volume.
You can adjust the volume of a group bus by selecting it and adjusting its volume fader in the deck. Because each group bus creates a mix of all the buses and events routed into it, this effectively reduces the volume of every event routed into that group bus.
You can adjust the volume of an arbitrary selection of events and buses by assigning all of them to a VCA and adjusting the volume of the VCA.