change css class of function with filter hook

I need to add a class to the dropdown topic select_class.
the original function is:

function bbp_get_form_topic_status_dropdown( $args = array() ) {

        // Parse arguments against default values
        $r = bbp_parse_args( $args, array(
            'select_id'    => 'bbp_topic_status',
            'select_class' => 'bbp_dropdown',
            'tab'          => false,
            'topic_id'     => 0,
            'selected'     => false
        ), 'topic_open_close_select' );

        // Filter & return
        return apply_filters( 'bbp_get_form_topic_status_dropdown', ob_get_clean(), $r, $args );
    }

I tired to use this but didnt work

function custom_callback($args = array() ) {
    
        $r = bbp_parse_args( $args, array(
            
            'select_class' => 'my-class',
            
        ) );
        
        return  $r;

}
add_filter( 'bbp_get_form_topic_status_dropdown', 'custom_callback', 12, 2);