How to add a secondary controller for Zwave binding?

As @rlkoshak correctly stated a secondary controller essentially is just a remote to (directly) control devices.
If you used it to expand the device limit it was another primary controller.
You can’t use a secondary to be a hot standby backup of your primary controller (which I assume is what you’re after, but this is an instance of the XY problem, see #8 in How to ask a good question / Help Us Help You).