function my_check_tags( $apply_tags, $order ) {

    if ( wpf_has_tag( 'Purchased evaluation', $order->get_user_id() ) ) {

        $new_tag_id = wpf_get_tag_id( '2nd evaluation bought' );

        $apply_tags[] = $new_tag_id;

    }

    return $apply_tags;

}

add_filter( 'wpf_woocommerce_apply_tags_checkout', 'my_check_tags', 10, 2 );