Let's look at the Birthday Card campaign as an example. In the Campaigns tab, click "Birthday Messages."
Underneath the preview image for the campaign, click "Edit Message."
Hover your mouse over any section within the editor, and you will see the option to add a section above or below.
Clicking that gives you the option to insert a "YouTube Video" section.
You will need to create a youtube video to link to the campaign. Once completed, copy that unique Youtube link to your new video.
Paste your YouTube video link into the "Video Link" box.
You will now see an image populate, which is what YouTube shows as the image for the video. If you wish to use a different image, select "Upload my own."
Click "Insert" to insert the video section.
To save your birthday card campaign, scroll down to lower right-hand side of the window and click "Save Changes."
Finally, make sure to click "Save & Exit" in the actual campaign.