This is called the Featured Column Section in your theme.
To edit it, go to:
dashboard – appearance – customize – widgets – home main content area – AT Featured Column.
Click on the upside-down triangle and you’ll see the screen below:
Click upload image to change the background image of the section.
The recommended image size here is 1280 * 830 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 then choose the alignment and border color according to your preference.