This is not a personal interview question. Still due to the popularity of technology awareness, be prepared to answer this question in non-technical interview.
If you have zero experience in SQL, then you can get help from database administrator (DBA) to improve the performance of SQL query.
Sample answer is:
There many options to improve the performance of a SQL query. I can get the explain plan of SQL query and then we can review explain plan with senior members. Based on the review comments, we can come up with performance improvement options for the query.
If I am totally stuck, then I will consult DBA to learn the latest methods for Query Performance improvement.