The short answer is that Premiere can't do this itself. The longer answer is that you need a DAW (Digital Audio Workstation). If you have Premiere Pro, you also have Adobe Audition most likely which is the Adobe DAW. If not, then Audacity is the right move. I've got an Audacity audio editing tutorial linked in my sig below which has helped a lot of people with the mechanics of this. I also have Audition tutorials on the channel as well.