Store Search in the coupon theme

I am looking for the solution to the problem that, whenever we search something in the standard search ( I mean not the advance Search), the site only search the key words in the post title or custom post title or post. Here, in Coupon Theme, it looks the keyword only in the coupon.

But I want to include the the custom category, (‘store’ in this case) in the search taxonomy.

How can I do that ?