How can I add the Yoast Editor icon in the top nav of WordPress?

I have been told that using the Yoast Editor that appears in the top nav of the back end of WordPress is a really good user experience, but where can I find it and add it? At the moment I can only see the Yoast SEO section mid-way down the screen in the backend of WordPress, not on the right-hand side of the top nav, which is the tool I want. Can anyone help me find it?