The Tempo button is available on both the app bar and the floating buttons.
Tap Tempo to start the metronome, and tap again to stop it. The metronome flashes and/or clicks at the song’s Tempo (BPM).
Press and hold Tempo to open Set Tempo.
Under Metronome Behavior you choose whether you hear a tick, whether the Tempo button flashes, whether the app bar flashes, the flash color, and whether the metronome starts at app startup or only when you tap Tempo.