Just click the green flag, works best in Turbo Mode. (Shift click flag for turbo mode) Adjust the Pitch and the Octave to change how the song sounds.
Credit to DogResidue for sprite. And Toby Fox for the song, sprite art, background, etc. UPDATE: I realized there were some parts of the song that were either off key or timed incorrectly, so I redid it using the correct notes and more broadcasts. That way even if it does get behind a little, it wont stay that way for long. Here's the new one I did. https://scratch.mit.edu/projects/238083966/