In the KB Admin Tools, go to Settings > Searching / Sorting.

Expand the panel for your internal and/or external site, depending on which you want to update. Check the box for Semantic search to enable it for the site in question.

If desired, you can also use the following dropdown to adjust the number of Semantic search max responses. This controls how many semantic search results will be displayed before the traditional keyword/title search provides any remaining matches.

Click Update to save your changes.