There's no such feature in v6. If you want to use this you have to do it manually.
Please not that anchor link support in mail clients is not great. You can see an overview here: https://www.caniemail.com/features/html-anchor-links/
If you still want to use it:
In the toolbar of the text editor click on the "<>" icon. It will show you the html of your content block. There you can add your id to the element you want. Considering not all mail clients support id="youranchor" is suggest you use id="youranchor" name="youranchor"