Google brought me to this old post
I am assuming you mean adding a title tag to an anchor text inside of the CMS rich text field?. If this is so I too am curious if there is a feature for this as I have looked all over the Webflow forums and have turned up nothing.
If you mean about the CMS item itself simply add a plain text field labeled “meta title” then go into the CMS page template settings and select it from the drop down in SEO Settings.
Blockquote a good example of that is here: Dynamic SEO and Open Graph Settings