There's not an easy one-step method that I know of, but you could do this.
Use SPLIT - COMPONENT CHANNELS to make 2 separate files that will be labeled left and right.
Go into each and use LEVELS -STEREO PAN and select "Pan all the way to the left" or "Pan all the way to the right". The one that's labeled right channel, pan that to the left; and the one labeled left, pan to the right. Copy one of those files and then paste mix it back with the other and re-save either as original file or to a new file if you want to preserve the original.