Either you would look for the keys.txt online (they are copyrighted so they cannot be shared here, even through PM) or you can generate them with another homebrew application named kezplez. More specifically, I am referring to
shchmue's fork since it is more stable and works on higher firmwares.
Also I would say you have a greater chance of being struck by lightning than breaking/destroying the console by installing a .XCI game
--------------------- MERGED ---------------------------
Outside of dumping the update/downloading it from online then installing it into the second console, you can try following this tutorial to share the update from one Switch to another:
https://gbatemp.net/threads/match-v...going-online-on-cfw-need-two-switches.509395/