Cacher is the code snippet organizer for pro developers

function wpse188669_pre_get_posts( $query ) {

   if (

       ! is_admin()

&& $query->is_main_query()

&& $query->is_search()

   ) {

       $query->set( 'post_type', array( 'product' ) );

       // set your parameters according to

     // https://codex.wordpress.org/Class_Reference/WP_Query#Taxonomy_Parameters

       $tax_query = array(

           array(

               // likely what you are after

               'taxonomy' => 'product_cat',

               'field'   => 'slug',

               'terms'   => 'category-2',

               'operator' => 'NOT IN',

           ),

       );

       $query->set( 'tax_query', $tax_query );

}

}

add_action( 'pre_get_posts', 'wpse188669_pre_get_posts' );