how change my menu on submenu

You can add a sub menu like below.

  // Call Terms_and_conditions_menu is function which load plugin menu
    add_action( 'admin_menu', 'Terms_and_conditions_menu' );

    // Add to WordPress admin menu
    if( !function_exists("Terms_and_conditions_menu") )
    {
    function Terms_and_conditions_menu(){

      $page_title="WordPress Extra Post Info";
      $menu_title="Terms And Conditions";
      $capability = 'manage_options';
      $menu_slug  = 'terms-post-info';
      $function   = 'terms_post_info_page';
      $icon_url="dashicons-media-code";
      $position   = 4;

      add_menu_page( $page_title,
                     $menu_title,
                     $capability,
                     $menu_slug,
                     $function,
                     $icon_url,
                     $position );

    add_submenu_page( $menu_slug,'sub page', 'menu title',$capability, 'my-secondary-slug');

    function my-secondary-slug(){

      echo 'Page text';
    }