Add additional menu items to the existing menu. In this case it's adding My Account page with endpoints as submenus.

additional_menu_items.php

<?
// Check if the WooCommerce plugin is activated.
if (in_array('woocommerce/woocommerce.php', get_option('active_plugins')) ) {
    add_filter( 'wp_nav_menu_items', 'add_loginout_link', 10, 2 );
}
/**
 * Add login/my account link
 *
 * Adding additional link to header menu. Be sure that your menu location is named
 * header-menu, othervise this won't work.
 *
 * @param  string $items Additional menu items to append.
 * @param  object $args  Menu arguments object.
 * @return string        Menu items modified.
 * @since  1.0.0
 */
function add_loginout_link( $items, $args ) {
    if ( $args->theme_location == 'header-menu' ) {
        if ( is_user_logged_in() ) {
            // WooCommerce endpoints.
            $orders           = wc_get_endpoint_url( 'orders', '', get_permalink( woocommerce_get_page_id( 'myaccount' ) ) );
            $edit_account     = wc_get_endpoint_url( 'edit-account', '', get_permalink( woocommerce_get_page_id( 'myaccount' ) ) );
            $addresses        = wc_get_endpoint_url( 'edit-adresses', '', get_permalink( woocommerce_get_page_id( 'myaccount' ) ) );
            $payment_methods  = wc_get_endpoint_url( 'payment-methods', '', get_permalink( woocommerce_get_page_id( 'myaccount' ) ) );
            $hours_spent      = wc_get_endpoint_url( 'hours-spent', '', get_permalink( woocommerce_get_page_id( 'myaccount' ) ) );
            // Build menu item with subitems.
            $items .= '<li class="menu_iem_logout"><a href="' . get_permalink( woocommerce_get_page_id( 'myaccount' ) ) . '">' . esc_html__( 'My Account', 'mytheme' ) . '</a>
                <ul class="submenu">
                    <li><a href="' . esc_url( $orders ) . '">' . esc_html__( 'Orders', 'mytheme' ) . '</a></li>
                    <li><a href="' . esc_url( $edit_account ) . '">' . esc_html__( 'Account Details', 'mytheme' ) . '</a></li>
                    <li><a href="' . esc_url( $addresses ) . '">' . esc_html__( 'Addresses', 'mytheme' ) . '</a></li>
                    <li><a href="' . esc_url( $payment_methods ) . '">' . esc_html__( 'Payment Methods', 'mytheme' ) . '</a></li>
                    <li><a href="' . esc_url( $hours_spent ) . '">' . esc_html__( 'Hours Spent', 'mytheme' ) . '</a></li>
                    <li><a href="' . esc_url( wp_logout_url( home_url() ) ) . '">' . esc_html__( 'Logout', 'mytheme' ) . '</a></li>
                </ul>
            </li>';
        } else {
           $items .= '<li class="menu_iem_login"><a href="' . get_permalink( woocommerce_get_page_id( 'myaccount' ) ) . '">' . esc_html__( 'Log In', 'mytheme' ) . '</a></li>';
        }
    }
    return $items;
}