Hi speedy,
If you right-click on the audio file and select ‘Sound Properties’ on the menu, there’s a ‘Channel/Speaker configuration’ which allows you to select what channel(s) to use.
If you’re using the stereo file and want a sepearate mono file, copy the stereo file to a new track and use ‘Convert to Unique Copy’ (Ctrl+U) before you change the channel/speaker configuration.