I am really sorry you did not received my replies. Both of the time i replied, may be ended in spam folder.

Please use following code in you theme’s (child theme’s if any) functions.php

add_action('asgarosforum_after_post_author', function( $user_id, $post_counter ){
    echo do_shortcode( '[fep_shortcode_message_to to="'. fep_get_userdata( $user_id, 'user_nicename', 'id') .'"]' );
}, 10, 2);