Adding authorized networks works similar to a firewall in that it allows specific networks to have access to the HTTPS endpoint for the cluster control plane. For more information, see the GCP documentation.
References:
https://cloud.google.com/kubernetes-engine/docs/how-to/authorized-networks
Changing the Network configuration is not possible after provisioning the GKE Cluster. Follow the steps below to create a new cluster with appropriate network configuration.
In GCP Console -
In Terraform -
References:
https://registry.terraform.io/providers/hashicorp/google/latest/docs/resources/container_cluster#nested_master_authorized_networks_config
https://cloud.google.com/kubernetes-engine/docs/how-to/creating-a-zonal-cluster