Ho do you set the following label in an already applied deployment?

kubectl label deployments my-deployment-v1 app=my-deployment

Is setting:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: my-deployment-v1
  labels:
    app: my-deployment

And I need, the following for a service to find it:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: my-deployment-v1
spec:
  template:
    metadata:
      labels:
        app: my-deployment