forward_btn

def next_song():
    next_song = song_box.curselection()
    next_song = next_song[0] + 1

    song = song_box.get(next_song)

    song = f'C:/gui/audio/{song}.mp3'
    pygame.mixer.audio.load(song)
    pygame.mixer.audio.play(song, loop=0)

    song_box.selection_clear(0, END)
    song_box.activate(next_song)

    song_box.selection_set(next_song, last=None)


forward_btn = Button(controls_frame, image=forward_btn_img, borderwidth=0, command=next_song)