got it by mail. great support
Open up the plugin file ‘custom-author-byline.php’ and edit line 72 which is-
//add_meta_box( ‘cab-new-meta-boxes’, ‘Custom Author Byline’, ‘cab_new_meta_boxes’, ‘custom_post_type’, ‘normal’, ‘high’ );
Remove the ‘//’ at the beginning of the line and change the ‘custom_post_type’ to the slug of your custom post type. Save the file and you should then have the box showing up on your custom post type pages.