Maybe one reason you didn’t get a response is because after watching 2 minutes of the sample video I still haven’t heard what you are asking about. Painful. But the process is simple. If the audio is separate from the video simply select it in the timeline, type “command-j” and chose a speed percentage of less that 100. If it’s still linked to the video, type “command-L” to unlink it first. There are also controls for having the audio change speed over time.
fledgling editor
professional slouch