"Run gcloud configurations list to start the Compute Engine instances". How the heck are you expecting to "start" GCE instances doing "configuration list".

Each gcloud configuration has a 1 to 1 relationship with the region (if a region is defined). Since we have two different regions, we would need to create two separate configurations using gcloud config configurations create

Ref: https://cloud.google.com/sdk/gcloud/reference/config/configurations/create

Secondly, you can activate each configuration independently by running gcloud config configurations activate [NAME]

Ref: https://cloud.google.com/sdk/gcloud/reference/config/configurations/activate

Finally, while each configuration is active, you can run the gcloud compute instances start [NAME] command to start the instance in the configurations region.

https://cloud.google.com/sdk/gcloud/reference/compute/instances/start