You may boot from a prepared USB.
Once booted, set the management IP from the console, and then access the webGUI.
When shown, enter the valid product key, and reboot.
After reboot enter the webGUI, and enter your active/active key.
Then, you may restore the settings and configuration from MAINTENANCE-->Misc page in the webGUI. Reboot, and activate the product.
You should be able to join the cluster then.