mist sync is used when you have such a custom installation of that keeps all of the data in a yaml file In case you want to sync your local db.yaml with your account in you could use the sync action:

mist sync dbyaml --dbyaml /path/to/local/db.yaml

mist sync will only add Keys and Backends that are added in your local installation and not in the service. It will not remove Backends and Keys that are added in the service and are absent in your local installation.