UPDATE: Following your comment, it is not currently possible to change the default registry, see this issue for more info.
You should be able to do this, substituting the host and port to your own:
docker pull localhost:5000/registry-demo
If the server is remote/has auth you may need to log into the server with:
docker login https://<YOUR-DOMAIN>:8080
Then running:
docker pull <YOUR-DOMAIN>:8080/test-image