Pair the speaker or headphones in your device's own settings. There is nothing to switch on inside iReal Pro. Bluetooth costs battery, so turn it off again after practice.

 

If the first beat of the count-in is missing, the speaker was asleep. iReal Pro plays a brief, almost inaudible sound before each song to wake it. AirPods are skipped, since they do not have the problem.

 

On Mac, open Preferences > General and set Wireless Wake Delay, anywhere from 0 to 1500 ms. It starts at 0, because macOS keeps the Bluetooth link awake on its own. Raise it if the first beats are still clipped. Windows has no such setting.

 

For the full guide, see Sound output and audio devices on the iReal Pro website.