Go to your teachable course and show the page where videos are.
Now open your Browser's console. For example in Chrome you can press F12 to open it.
Paste the following code in the console
$('.attachment-wistia-player').each(function () { console.log($(this).attr('data-wistia-id')); });
Press enter to retrieve all videos IDs that are present in the opened page. For example: