docker unable to push repo access denied

# you may need log out first `docker logout` ref. https://stackoverflow.com/a/53835882/248616
docker login

docker tag firstimage YOUR_DOCKERHUB_NAME/firstimage

docker push YOUR_DOCKERHUB_NAME/firstimage

You need to include the namespace for Docker Hub to associate it with your account.
The namespace is the same as your Docker Hub account name.
You need to rename the image to YOUR_DOCKERHUB_NAME/docker-whale.