add_submenu_page('index.php', __('Plugin Name from page', 'pluginname'), 'Plugin Name', 'manage_options', 'pluginname-hello', 'you_call_function' );
pluginname-hello – The slug name to refer to this menu by (should be unique for this menu).
you_call_function – The function to be called to output the content for this page.
More information:
https://developer.wordpress.org/reference/functions/add_submenu_page/