I know I can restart an app with:
aptible restart --app "APP_NAME" --environment "ENV_NAME"
as per this doc, but have not been able to find documentation on how to do it at the service level…
There is not a specific command to do so at this time, however you can leverage the scale operation to accomplish this. Just pass the current number of containers for your service, and it will have the same effect as restarting just this service:
aptible apps:scale --app $APP $SERVICE --container-count $CURRENT_NUMBER