Add provisioned machine to juju controller

I am deploying OpenStack using Juju Charms. I had a juju controller node deployed under MAAS without HA and it went down one day because of hardware failure. Now I have rebuild the juju controller node but wonder how can I connect the provisioned machine under the new controller.

I tried add-machine command but it turns out my machine has already provisioned.

juju add-machine ssh:ubuntu@
ERROR machine is already provisioned