It is not possible to use the external-event directive in My Account templates.
You can either use the custom event directive as described here or in order to push custom events from the My Account iframe to your website's front-end application, you would need to use post messages.
For example, if you'd like to listen to a click on the "Add Credit Card" button, you can add the following code to the My Account Wallet Components template:
XML
<t onclick="parent.postMessage('Add Credit Card Event', '<your_website_url>/myaccount.html');">Add Credit Card</t>
And replace the <your_website_url> with the URL of your website where you'd like to receive the post messages.