During the stereo pairing process in the Sonos app, you choose which speaker acts as the left and which speaker acts as the right.

Is that part of the “tuning” setup where sounds are generated and I would use my phone to listen to them?  I’ve had my speakers quite a while and just moved them to a different room and don’t remember going through setup before, although I probably did.  Also, with 2 speakers does horizontal and vertical come into play, and if so, how?  I’m not sure I understand.  Thanks!

No, it’s part of the pairing process in the Sonos app:

https://support.sonos.com/s/article/1066?language=en_US
 

You can separate the stereo pair by following these steps:

https://support.sonos.com/s/article/4825?language=en_US
 

After separating the pair, redo the pairing process above and choose which speaker will act as the left and which speaker will act as the right. After pairing them, redo Trueplay tuning to optimize the sound in the new room.

Most users keep the speakers in a vertical orientation when used as a stereo pair. 

The tweeters are located on the logo side of the speaker. So the “inside” position would produce a tighter stereo image. The “outside” position would produce a wider stereo image. Choose whatever sounds best to you.

Thank you!  I really appreciate your assistance!

If the speakers are already stereo paired, an easier way to check which is left and which is right is to adjust the L/R balance under the EQ settings in the Sonos app.