Paste the code to your WP Engine website’s HTML field.
Next, go to your WP Engine website editor and find the HTML field. It is most likely in the form of an HTML/Code widget or module which you can find on the WP Engine’s editor. Add it to your page, and paste the Mastodon Feed Embed Code you’ve copied before to the HTML field.
Save and update, and that’s it, you should have Common Ninja’s Mastodon Feed plugin on your WP Engine website.