Just been looking to disable the reactivation lock on my Note 8 before sending it back but it doesn't seem to be there, checked Note 9 and it's the same, have they done away with this now on the newer devices?
Signing out of all accounts then resetting it should do the trick. You can test by going through the setup and try skipping the account login, it should let you if you did it right. Then just reset it again and send it back.
It's also possible that resetting the device from within the OS would work as well, since it detects that you had access to the screen unlock info. It may be more of a protection against resetting through Recovery.