In this short video tutorial, tdcat.com shows how to make a stereo track behave like a mono track using the Fill Left/Fill Right audio effects in Premiere Pro. Very useful if you've got a stereo clip, and one of the channels is the onboard camera audio.

Short tutorial on how to use one channel of a stereo track in Adobe Premiere Pro or make a dual mono track. This is useful to force a stereo vocal track to mono or use maybe only the left channel when the right channel has a different mic source. —tdcat.com