This is called the Featured Section in your theme.
It can be used to display a call to action in the middle of the homepage.
To edit it, go to:
dashboard – appearance – customize – widgets – home main content area – AT Featured Section
Click on the upside-down triangle and you’ll see the screen below:
Click upload image to change the background image of the section. Use an image with a size of 1920 x 770 pixels.
You can change the Title, Description, and Button Text to suit your free offer.
Copy and paste the link to your landing page where it says Button Link URL.