To make a docker image available for deployment you must publish it to a docker registry. If you already have a local registry for offline installations you can use that to store your images. Otherwise, you have to create your own (local) registry according to https://docs.docker.com/registry/deploying/.
If you want to create a local docker registry on your development computer, it is recommended to use a different port than 5000 for your local registry since this port is also used when starting an agent via VisualStudio.
Assuming that you have a registry running on localhost:5555, you must then choose a registry tag, tag your local image with the following command
docker tag <image name>:<image tag> localhost:5555/<registry tag>
and push it to the registry
docker push localhost:5555/<registry tag>
For further information see also https://docs.docker.com/registry/deploying/.