My first post disappeared…
Anyhow, you can right-click your clip in the bin. Select Modify, Audio. Then you can select to change your stereo track to 2 chn mono. You’ll then have to re-edit into your sequence. Unless you have cut the clip a hundred different ways, it’s pretty easy. Select your first frame of the clip in your sequence, turning on that layer, and select match frame. Then edit it back into your sequence. Not sure of a better way to do that. Do it for all instances that clip was edited into your sequence.
Good Luck!
TC