If you want to remove country field which is available in traveler form in checkout page, please add following given code in functions.php file of your child theme.

function wp_travel_remove_country( $checkout_fields ){

    unset( $checkout_fields['traveller_fields']['country'] );
    return $checkout_fields;
}

add_filter('wp_travel_checkout_fields', 'wp_travel_remove_country' );

Before:

After Removing Field:

Also, regarding creating child theme, please refer link.

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