JSFiddle - React, Tailwind, and code Playground

HTML

<div class="form-group required">
    <input type="text" name="postcode" value="" placeholder="Coloque seu CEP" id="input-order-postcode" class="form-control" />
</div>
<div class="form-group required">
    <select name="country_id" id="input-order-country" class="form-control country-selector" data-post-code-required="#input-order-postcode" data-zone="#input-order-zone">
        <option value="" selected="selected"> --- Selecione o País --- </option>
        <option value="30">Brasil</option>
    </select>
</div>

<div class="form-group required">
    <select name="zone_id" id="input-order-zone" class="form-control">
        <option value="" data-sigla='' selected="selected"> --- Selecione o Estado --- </option>
        <option value="440" data-sigla='AC'>Acre</option>
        <option value="441" data-sigla='AL'>Alagoas</option>
        <option value="442" data-sigla='AP'>Amapá</option>
        <option value="443" data-sigla='AM'>Amazonas</option>
        <option value="444" data-sigla='BA'>Bahia</option>
        <option value="445" data-sigla='CE'>Ceará</option>
        <option value="446" data-sigla='DF'>Distrito Federal</option>
        <option value="447" data-sigla='ES'>Espírito Santo</option>
        <option value="448" data-sigla='GO'>Goiás</option>
        <option value="449" data-sigla='MA'>Maranhão</option>
        <option value="450" data-sigla='MT'>Mato Grosso</option>
        <option value="451" data-sigla='MS'>Mato Grosso do Sul</option>
        <option value="452" data-sigla='MG'>Minas Gerais</option>
        <option value="453" data-sigla='PA'>Pará</option>
        <option value="454" data-sigla='PB'>Paraíba</option>
        <option value="455" data-sigla='PR'>Paraná</option>
        <option value="456" data-sigla='PE'>Pernambuco</option>
        <option value="457" data-sigla='PI'>Piauí</option>
        <option value="458" data-sigla='RJ'>Rio de Janeiro</option>
        <option value="459" data-sigla='RN'>Rio Grande do Norte</option>
       ...

JavaScript

$('input#input-order-postcode').on('change', function() {
    if (this.value) $('select').val('');
});