You have complete control over what tables MinusX can see and use to answer your queries, for every database on Metabase. You can find the list of tables via the "Tables" quick action.

All tables available in the database are listed here. The tables selected by default are ones that are relevant to you, based on your past queries. You can search and select/deselect tables. The final selected list is what is exposed to MinusX.

Your selection is saved, and used in every subsequent query. You can always check tables in context in the Context tab in the settings pane.