You have set up a Compute Engine VM instance as a NAT gateway and created a route with the following command:

gcloud compute routes create no-ip-internet-route \  
--network custom-network1 \  
--destination-range 0.0.0.0/0 \  
--next-hop-instance nat-gateway \  
--next-hop-instance-zone us-central1-a \  
--tags no-ip \  
--priority 800  

To ensure existing instances use this NAT gateway, what command should you run next?