Hi!
By default, the plugin should return only the post types selected under the General Options -> Sources panel: https://i.imgur.com/Qh6Vazb.png
Was the search executed via the plugin search field?
If yes, and the override is still not working, you can still try this option.
If it is still not working, then there is very likely a custom query somewhere in the search template file, or in the theme functions.php file. There is certainly a way to exclude post types from that query, however it depends on the implementation – so you may need to ask the theme author about that.
