Once you move all the Link to Primary ative role switch and tested, you can simply turn off the seconday switch and move to new location.
Things to check before you bring secondary, make sure you SVL Links and DAD links working as expected. then connect the cable or turn on the device and connect the cable, the seconday device detects primary and (secondary reboot automatally join SVL).
Once the Secondary come online working as expected, When you ready to move Primary flip the role from redundancy to primary, turn off and move the device(by this i expecte you moved the link to other site)
below some reference guide :
https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-9000/nb-06-cat-9k-stack-wp-cte-en.html
Note : Offload the config out of the box all time and do this task always in Maintenance window.