Here’s how to move a VM to another VPC.
Stop VM.
gcloud compute instances stop $INSTANCE_NAME \ --zone $ZONE_NAME \ --project $PROJECT_ID |
Move VM to another VPC.
gcloud compute instances network-interfaces update $INSTANCE_NAME \ --zone $ZONE_NAME \ --network-interface=nic0 \ --network $YOUR_NETWORK \ --subnetwork $YOUR_SUBNETWORK \ --project $PROJECT_ID |
Start VM.
gcloud compute instances start $INSTANCE_NAME \ --zone $ZONE_NAME \ --project $PROJECT_ID |