How do i make 2 channels into 1

[Chris B]

Can I ask the audience?
(I presume that's your reference?)

[Chuck Engels]

Yes, I couldn't resist

[Chuck Engels]

I just had to do this recently, got a wedding tape with only one channel recorded.
I unlinked the audio and video, duplicated the audio, applied the swap channels effect to the duplicated clip and there you have it, a mono signal split over two channels.
Thanks to this thread, it helped a lot