Forse intendi qualcosa del genere ?

codice:
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <form action="#" method="post">
        <input type="text" id="cdSezi" value="REF.">
        <select id="idtpCircolazione" name="tpCircolazione">
            <option value="D">DISTRIBUTORE</option>
            <option value="I">INTERNA</option>
            <option value="L">LIBERA</option>
            <option value="N">NO</option>
            <option value="O">Disponibile online</option>
            <option value="Y">Escluso ILL/ISS a tempo</option>
            <option value="Z">Escluso ILL/ISS definitivo</option>
        </select>
    </form>

    <script>

        const select = document.getElementById('idtpCircolazione')
        const ref = document.getElementById('cdSezi')
        const optionI = Array
            .from(select.children)
            .filter(option => option.value.includes('I'))

        function controllaMovimentiInve() {
            ref.value == 'REF.'
                ? optionI[0].setAttribute('selected', '')
                : optionI[0].removeAttribute('selected')
        }
        controllaMovimentiInve()
        ref.addEventListener('input', controllaMovimentiInve)

    </script>
</body>

</html>