You can use Joomla Menu Manager to edit items in this menu. Please go to Administration >> Menus >> Kunena Menu >> Help to edit or remove this menu item.
In this menu item you can use Plain Text, BBCode or HTML. If you want to bind article into this page, you may use article BBCode (with article id):
If you want to create your own menu for Kunena, please start by creating Home Page first. In that page you can select default menu item, which is shown when you enter to Kunena.