<div id="viewer"></div>
<select id="models"></select>

#viewer {
  position: absolute;
  inset: 0;
}

#models {
  position: absolute;
  left: 1em;
  top: 1em;
  z-index: 1;
}

import { initViewer, listModels, loadModel } from 'https://aps-codepen.autodesk.io/utils.js';

const viewer = await initViewer(document.getElementById('viewer'), { extensions: ['Autodesk.DocumentBrowser'] });
const models = await listModels();
const dropdown = document.getElementById('models');
dropdown.innerHTML = models.map(m => `<option value="${m.urn}">${m.name}</option>`).join('');
dropdown.onchange = () => dropdown.value && loadModel(viewer, dropdown.value);
dropdown.onchange();