Directorypress Reassign Authors is a WordPress plugin by anshulsojatia that allows directorypress site administrators to change the authors of the listings. Just upload a valid CSV file and let the plugin to its work.
DirectoryPress is a WordPress premium theme that can help you setup your directory website within a few minutes.
Plugin homepage: GeekTrick.com
Download: http://wordpress.org/extend/plugins/directorypress-reassign-authors/