I am using gcp and kubernetes.
I have gcp repository and container registry.
I have a trigger for build container after pushing into the master branch.
I don't know how to set some auto-trigger to deploy new version of the container (docker file).
How can I automate the build process?
There are two solutions here.
You can expand the build step. Cloud Build can also push changes to your GKE cluster. You can read more about this here
What you currently have is a solid CI pipeline, for the CD, you can use Spinnaker for GCP, which was released recently. This integrates well with GCE, GKE and GAE and allows you to automate the CD portion.
You need some extra pieces to do it, for example if you use Helm to package your deployment you can use Flux to trigger the automated deployment.