Navigate to Settings > Prefooter to add and update your prefooter content. The prefooter on Gospel.io shows up just before the footer on almost all pages. Here is a visual example from Olivet:
(The prefooter is the green box above the footer).
From the settings page, you can update the title (stay in touch), the blurb, the image, and the button label (Get the newsletter).
When you are done, hit 'Publish' to save your changes, and you're done! You should see the changes reflected on your live website in about ten minutes.