Timezone switcher in JS compatible with older browsers [closed]

I’m trying to create SELECT box that changes all dates (yyyy-mm-dd hh:ii) on a page containing unformatted HTML

There is some problem assigning value to formattedDate

EDIT: the code works only in newer browsers, so I’d like to make it compatible with say 2014 browsers.

  function switchTZ() {
    const tz = document.getElementById("tz").value;
    const updatedText = document.body.innerHTML
      .replace(/b(d{4}-d{2}-d{2}) (d{2}:d{2})b/g, (match, datePart, timePart) => {
        const local = new Date(datePart+'T'+timePart+':00+01:00');
        const formattedDate = new Intl.DateTimeFormat('en-GB',
        {
          timeZone: tz,
          year: 'numeric',
          month: '2-digit',
          day: '2-digit',
          hour: '2-digit',
          minute: '2-digit',
          hour12: false
        }).format(local);
        return formattedDate.replace(",", "");
      });
    document.body.innerHTML = updatedText;
  }

<select id="tz" onchange="switchTZ()">
  <option value="America/Mexico_City">America/Mexico_City</option>
  <option value="America/New_York">America/New_York</option>
  <option value="America/Sao_Paulo">America/Sao_Paulo</option>
  <option value="Asia/Seoul">Asia/Seoul</option>
  <option value="Asia/Tokyo">Asia/Tokyo</option>
  <option value="Europe/Berlin">Europe/Berlin</option>
</select>
<p>27807;2023-10-20 01:30<br />27808;2023-10-21 01:30</p>