Did you back up your device prior the installation? If yes, Use the backup advance function and restore the BlackBerry Messenger database. This is with Desktop Manager v4.6. Generally DM would automatically take a device backup with the file name similar to LoaderBackupxxxx.ipd. If you had not explicitly taken a backup, try the backup file name I just mentioned.
Without a backup you will have to manually add them again by send requests via BBM.