If you are willing to rename ‘Search’, ‘Trip Type‘, ‘Location‘ labels displaying in search widget, please add following given code in functions.php file of your child theme.

function customized_strings( $strings ) {
    $strings['trip_type'] = __( 'Your Trip type', 'wp-travel' );
    $strings['search'] = __( 'Your Text', 'wp-travel' );
    $strings['location'] = __( 'Your Location', 'wp-travel' );
    return $strings;
}
add_filter( 'wp_travel_search_filter_label_strings', 'customized_strings' );

Also, regarding creating child theme, please refer link.

If you have any queries, please submit it to our Contact page.