...
To enable it, click the toggle in the search box, either on the Home Page or Search Results page
Enter your search keyword(s) in the What are you looking for? box and press Return or Click the Search icon. For example, if you enter water and click Search, you might see the additional terms shown below
You can remove any of these terms by clicking the X next to it before you run the query again.
...
Query Expansion Settings
You can specify a different engine for calculating similarity and you can also adjust the similarity threshold for query terms:
...
Go to Manage Voyager > Index > Query Settings > Query Expansion
Adjust the Similarity threshold (minimum 0; maximum 100) by entering a new value in Set Minimum Similarity Score (30-50% are recommended). Any terms that fall below the threshold will not be used in the expanded query
You can enter a new similarity engine by clicking Edit next to Wikipedia Query-Expansion Model. Usually this will be one based on your particular data set and data types.
Click Save when you are done