OnSong can perform actions such as starting autoscroll using triggers. Triggers are events that happen, such as touching the screen or pressing a foot pedal. Another type of trigger is when the song is changed in the Song Viewer.  This is called a Song Change Trigger.

You can set the action of the Song Change Trigger by going into the Utilities Menu by tapping on the gear icon in the Menubar.  Next, open Settings and choose Navigation Settings on the left and find the Triggers section on the left.  Locate the Song Change Trigger and tap to open the Actions Menu.  From there you can choose Autoscroll > Control > Start.