Have you tried from OnSong forum/manual/support? 
With MobileSheets (similar to OnSong) I just mark that which midi command does what action 
Then I just make sure that MM is sending those commands (and that the text matches) 
I’m assuming it’s the same for OnSong but can’t comment on how to find these settings 
You also need to make sure that the MM command is going with Bluetooth (or cable) so that your device can receive it 
MobileSheets has midi diagnostic tool that shows what commands it’s receiving