There is a locked thread with an unacceptable answer (put a sticker :D)
I simply searched “surround test” from Youtube and played “5.1 Dolby Surround Test”.
The lady kindly announces “This is the right/left surround channel” from the specific speaker, and it was easy to switch the places (which were of course wrong way around after moving the house)…
Same applies for stereo pairs, equivalent stereo tests exist. Or then just use balance as somebody indicated in the “sticker thread”…