Add this into the top of the section in the “Text” tab:
<a name="this-section"><!-- anchor --></a>
Then linking to yoursite.com/whatever-page#this-section will take you there.
If the Add Section button isn’t working, try updating to the latest version of the plugin.
If that doesn’t work, try #1 on this page: https://generatepress.com/knowledgebase/debugging/