To use the iRig Blue Turn in OnSong, the pedal needs to be in Mode 1. Here are steps on how to accomplishing setting up the iRig BlueTurn.
1.) Go into the bluetooth screen on your device.
2.) Tap and hold on the up arrow and then switch the device on. Once on, there will be a blue flashing light going back and forth between the switches.
3.) Tap device on the list and pair.
4.) Open OnSong
5.) Tap on the Actions icon and find the iRig BlueTurn silhouette.
6.) Select actions wanted.
7.) Close down the foot pedal menu and you'll be able to perform the actions set.
In addition, here is the manual for the iRig BlueTurn: