Cloned consul cluster pointing to original cluster AWS

Hi All
we have deployed consul cluster and its executed using the run-consul script here (terraform-aws-consul/run-consul at master · hashicorp/terraform-aws-consul · GitHub)
What we are trying to do is create an AMI from the existing server and create a new cluster with 3 instances.
Now as soon as we start the new servers they attach themselves to the existing cluster even though the tag value has been changed to use a new cluster name.
We are not able to find anywhere where the config needs to be changed so that both clusters can be decoupled.
We can’t create a completely new cluster from scratch as we have secrets (transit) that won’t migrate and we can’t afford to decrypt and re-encrypt whole data in prod. Hence we need clone of existing one which we can then upgrade step by step

Any suggestions will be helpful.