HOW DO I GET CHANNEL 3 to be stereo?

Is it even possible to get Channel 3 or 4 et cetera to somehow be stereo. my interfaces channel 1 and 2 are not responding correctly so i am trying to find alternative ways to record from my record player. I searched the FAQ’s and couldn’t get a satisfying answer. thank you for your time, peace

If you pan one mono channel to the left and another to the right, then mix them, you will have a stereo track.
Tracks are mixed automatically when you Export, or you can do it manually, but the manual method depends on which version of Audacity you are using.