See the page on adding social icons to your emails if you haven’t yet created any social icons yet.

To add a clickable URL to any social icon layer in your design, click on the Social Icon Link layer you’d like to add a link to, then click the Settings button in the plugin header, and pasting your URL into the Clickable URL Link input field; this will ensure that your social icon opens up that URL in the browser when it’s clicked.

You can also set the alt text attribute by populating the Image Alt Text input field in the Settings panel, too.