[Zubersoft]

Long press your song, then tap Edit Song, go to the MIDI tab, tap the plus button on the right to add a new MIDI command, change the dropdown to "Control Change", enter 7 for number and enter your volume in the value field. That's all you need to do if you want to trigger the volume change when the song is loaded. Alternatively, you could assign that same command to a smart button and drop that button on your score. You could then tap the button when you want to change the volume.

Mike