Set default country in the booking form

To set a default country in the booking form paste this code in functions.php:

function hotelier_custom_default_country_address( $value, $input ) {
    if ( $input === 'country' ) {
        $value = 'IT';
    }

    return $value;
}
add_filter( 'hotelier_booking_get_value', 'hotelier_custom_default_country_address', 10, 2 );

And replace IT with your desired country code.