This is not an iframe, it's a script:
<script src="https://app.repairdesk.co/widgets/include.js?token=5674b74984008-686-5674b7498401d&height=1200&width=1000&scrolling=yes"></script>
You should use the "Custom Javascript" module with everything inside of the quotes after src as the "Script URL" with the "Script URL Position" set to "in the page at the position of this content instance".
Hope this helps,
Joe Davis