The page builder you’re using uses widgets.
You can use the Secondary Navigation add-on, you’d just need to change the position of it using PHP.
For example, set the Secondary Navigation to display after the header, then add this:
add_action( 'after_setup_theme','generate_secondary_nav_below_page_header' );
function generate_secondary_nav_below_page_header()
{
remove_action( 'generate_after_header', 'generate_add_secondary_navigation_after_header', 7 );
add_action( 'generate_after_header', 'generate_add_secondary_navigation_after_header', 15 );
}
Adding PHP: https://generatepress.com/knowledgebase/adding-php-functions/