You can make the Search Type drop-down list read-only for users of the front-end client, preventing them from performing a search other than the one preselected for them. (For more information on preselecting a query, see Preselect a Custom Query.)
To only display a single query, set the value of the showSingleQuery key in the SearchPanel object to true. To allow users to manually select other queries, set the value to false. For example:
"showSingleQuery": true