Hi there,
I just saw this while browsing. There are plenty of tutorials around for this as it is a wordpress method that works with GP. It involves anchor links and custom menus…
For example https://wordpress.org/support/topic/how-do-i-create-page-anchors-from-wordpress-menus
Last poster:
In HTML this is called a document fragment.
There are two steps. First you insert an anchor in your webpage:
<h2>Reviews</h2>
Then in Appearance > Menus, in the Custom Links box you put in the URL plus a pound sign plus the fragment name:
http://www.casafuturatech.com/smalltalk/#smalltalk-reviews
Then you can put the menu item anywhere in your menus.