These options are in order from best to worst.
If you can add HTML:
Just add the following HTML where you want the logo to appear in the email.
<img alt="Complete Recovery" src="https://email@example.com" width="339" style="width: 100%; max-width: 339px; font-family: sans-serif; color: #ffffff; font-size: 20px; display: block; border: 0px;" border="0">
If you are using a rich text editor that does not accept HTML:
Try selecting the following image like you would select text, then copy and paste it into the editor.
If neither of the above options works:
You can use the image URL below. Keep in mind that this is the worst option. This image will look blurry/blocky on mobile devices.