Adding menu’s to your WordPress theme > https://since1979.dev/snippet-003-adding-menus-to-your-theme/

snippet-003-show-menu-on-page.php

<?php
/**
 * Insert the "header-menu" into the page.
 *
 * @see https://since1979.dev/snippet-003-adding-menus-to-your-theme/
 *
 * @uses wp_nav_menu() https://developer.wordpress.org/reference/functions/add_action/
 * @uses array() https://www.php.net/manual/en/function.array.php
 */
wp_nav_menu(
    array(
        'theme_location' => 'header-menu',
        'menu_class' => 'your-own-class'
    )
);
?>