I have a one-minute clip, and in the first 5 seconds of it, there's audio of me asking a question. But I want to re-do just the audio part of that. How do I sort of "mute-out" that first 5 seconds of the "real" audio that is a part of the video, and, essentially, insert a "new" 5-seconds of a new audio file that I'll record [where I'll ask the question better]?