Add following code in your theme’s (child theme’s if any) functions.php
add_filter( 'fep_filter_get_message_with_replies', function( $args ){
$args['order'] = 'DESC';
return $args;
});
To show form on top, You have to edit view-message.php template. Instruction in https://www.shamimsplugins.com/docs/front-end-pm-pro/customization-front-end-pm-pro/change-templates/