To back up your Overseer data, navigate to the installation path where Overseer resides. By default this is c:\program files\overseer\
Find the overseer.db, overseersecure.db, and overseerdata.db, and copy them to your backup location. Overseer.db stores your configuration data, OverseerData.db stores information about the history of your resources, and OverseerSecure.db stores your passwords securely.
In the event that your Overseer installation becomes corrupt in some way, having these three files will allow you to pick up from the point when the last backup was performed.