Move the Australia state <optgroup> before the one for New Zealand https://eventespresso.com/topic/change-order-of-stateprovinces-optgroups-on-registration-forms/#post-201209

moveoptgroups.php

function my_move_australia_before_nz() {
    ?>
    <script>
    jQuery(document).ready(function($) {
        var aussie = '.ee-reg-qstn-state optgroup[label="Australia"]';
        var kiwi = '.ee-reg-qstn-state optgroup[label="New Zealand"]';
        $(aussie).insertBefore(kiwi);         
    });
    </script>
    <?php
}
add_action( 'AHEE__EE_Form_Section_Proper__localize_script_for_all_forms__begin', 'my_move_australia_before_nz' );