I'm sorry to hear you are having trouble. OnSong hides the menubar when you tap in the middle of the screen. You can have the menubar reappear by tapping in the middle of the screen again or by navigating to the top of your song and quickly swiping down on your song with your finger.
If you do not want the menubar to hide, you can go into the Utilities menu (gear icon) --> Settings --> Navigation Settings--> Menubar--> Prevent Menubar from Hiding to On. If you cannot access the menubar in the OnSong app to perform these steps, you can also access these settings from your iOS Device home screen by opening the Settings app on your device and choosing OnSong under Applications towards the bottom.