Perform these steps on each node:
Start the Cassandra-cli connected  to your node.
Run the following:
  1. use system;
  2. set LocationInfo[utf8('L')][utf8('ClusterName')]=utf8('Brisk Cluster');
  3. exit;
  4. Run nodetool flush on this node.
  5. Update the cassandra.yaml file for the cluster_name
  6. Restart the node.
Don't forget to kept the the default cluster name Test Cluster  while performing the initial operations

Regards,
Abhijit