How to create a Tools menu on the Network Admin dashboard from a plugin

I want to put a Tools menu item on the Network Admin dashboard

If you meant under the core top-level “Dashboard” menu as seen on the following screenshot, then you can use the network_admin_menu hook along with add_submenu_page() to add your menu item.

Or if you wanted a top-level menu like the following, then use the same hook as above, but use add_menu_page() to add the menu, and then use add_submenu_page() to add menu items (i.e. submenus) to that top-level menu.

Full Working Example

<?php
/**
 * Plugin Name: WPSE 391799
 * Description: Network Admin custom "Tools" menus
 * Version: 1.0
 */

// Adds the custom Network Admin menus.
add_action( 'network_admin_menu', 'wpse_391799_add_network_admin_menus' );
function wpse_391799_add_network_admin_menus() {
    add_submenu_page( 'index.php',      // parent slug or file name of a standard WordPress admin page
        'My Tools Page',                // menu page title
        'My Tools (Submenu)',           // menu title
        'manage_network',               // user capability required to access the menu (and its page)
        'my-tools-page',                // menu slug that's used with the "page" query, e.g. ?page=menu-slug
        'wpse_391799_render_tools_page' // the function which outputs the page content
    );

    add_menu_page( 'My Tools Page',      // menu page title
        'My Tools (Top-Level)',          // menu title
        'manage_network',                // user capability required to access the menu (and its page)
        'my-tools-page2',                // menu slug to that's with the "page" query, e.g. ?page=menu-slug
        'wpse_391799_render_tools_page', // the function which outputs the page content
        'dashicons-admin-tools',         // menu icon (in this case, I'm using a Dashicons icon's CSS class)
        24                               // menu position; 24 would place the menu above the "Settings" menu
    );

    add_submenu_page( 'my-tools-page2',
        'My Tools Submenu Page',
        'My Tools Submenu',
        'manage_network',
        'my-tools-submenu-page',
        'wpse_391799_render_tools_submenu_page'
    );
}

// Outputs the content for the "My Tools (Submenu)" and "My Tools (Top-Level)" pages.
function wpse_391799_render_tools_page() {
    ?>
        <div class="wrap my-tools-parent">
            <h1><?php echo esc_html( get_admin_page_title() ); ?></h1>
            <p>Foo bar. Bla bla. Your content here.</p>
        </div>
    <?php
}

// Outputs the content for the "My Tools Submenu" page.
function wpse_391799_render_tools_submenu_page() {
    ?>
        <div class="wrap my-tools-submenu">
            <h1><?php echo esc_html( get_admin_page_title() ); ?></h1>
            <p>Foo bar. Bla bla. Your content here.</p>
        </div>
    <?php
}