Do you mean the
<title> tag that appears in your browser tab?
GP doesn’t do anything to these titles, we rely solely on WP or plugins like Yoast to change them for you.
Have you checked out this article?: https://yoast.com/wordpress-seo/#titles
If it’s not working as it’s shown, you might want to check with their support to see if they have any ideas.
Let me know if you need more info 🙂