Create an alias of the image
Use docker tag to create an alias of the image with the fully qualified path to your registry. This example specifies the samples namespace to avoid clutter in the root of the registry.
docker tag nginx myregistry.azurecr.io/samples/nginx
Push the image to your registry
Now that you've tagged the image with the fully qualified path to your private registry, you can push it to the registry with docker push:
docker push myregistry.azurecr.io/samples/nginx
Reference:
https://learn.microsoft.com/en-us/azure/container-registry/container-registry-get-started-docker-cli