This plugin provides nothing more than a very simplistic direct DB access tool in the admin console under Server -> Server Management. It's purpose is to allow admins to work with their DBs during debugging sessions to try to determine the state of their DB and maybe make minor adjustments. It should NOT be used normally and you should never edit your DB while Openfire is running without knowing absolutely what you are doing. Openfire caches a lot of data in the backend and changing things out from under it will confuse it and probably cause a wealth of problems. Most likely if you are installing this, it's because someone asked you to. =)
Copy dbaccess.jar into the plugins directory of your Openfire installation. The plugin will then be automatically deployed. To upgrade to a new version, copy the new dbaccess.jar file over the existing file.