Thank you @BenW, this worked great!
I ended up with the following scripts to get this all working.
Start up a docker image
docker run -it -p 5080:5080 -p 6080:6080 -p 8080:8080 -p 9080:9080 -p 8000:8000 -v $DGRAPH_LOCATION:/dgraph --name dgraph dgraph/standalone:v21.03.0
Run an existing docker image (eg after one has been created)
docker run -it -v $DGRAPH_LOCATION:/dgraph -p 8000:8000 -p 8080:8080 -p 9080:9080 $DOCKER_IMAGE
Export Data
curl -g -X POST "${GRAPHQL_API}"/admin -H "Content-Type: application/json" -d '{"query": "mutation { export(input: { format: \"json\" }) { response { code message } } }"}'
Import Data
docker exec -it "$DOCKER_CONTAINER" dgraph live --files "$BACKUP_FILE_FULL_PATH"
Drop Current Data and Import Data
curl -X POST "${GRAPHQL_API}"/alter -d '{"drop_op": "DATA"}'
docker exec -it "$DOCKER_CONTAINER" dgraph live --files "$BACKUP_FILE_FULL_PATH"
And examples of the variables
GRAPHQL_API=localhost:8080
BACKUP_FILE_FULL_PATH=/Users/<computer-user>/<my-repo>/dgraph/docker/export/<folder-with-export>/g01.json.gz
BACKUP_FILE=export/<folder-with-export>/g01.json.gz
DGRAPH_LOCATION=/Users/<computer>/<my-repo>/dgraph/docker
DOCKER_IMAGE=<docker-image-id>
DOCKER_CONTAINER=<docker-container-id>