If your VM instance uses the primary network interface, you can enable or disable PTR records by updating the access configuration on the primary network interface, 'nic0', for the VM instance.
If your network access is not configured, add the access config, then enable PTR records within the network interface menu.
Use the gcloud compute instance update-access-config command to add a PTR record to an existing access configuration.
gcloud compute instances update-access-config [INSTANCE_NAME]
--public-ptr --public-ptr-domain [DOMAIN_NAME]