The easiest way to find your campaign’s HTML is to open the Archive link for the campaign.
You can find that by going to Email > Campaigns in the left-hand navigation. Then, click the three dots on the right side of the campaign name, and choose View.
Using your Internet browser, find the option to View Source. Each browser varies as to where they put it, but here are examples in both Safari and Chrome.
Click Develop > Show Page Source.
Note: You will need to go into Safari’s Preferences > Advanced and click Show Develop menu in menu bar if you haven’t already. This will make Develop appear in your menu.
Click View > Developer > View Source.