Each of your pages in your website builder can have a different header background image. To set the header background image for a page, please follow these steps:

1. Sign in to your Dynadot account.
2. Select "My Websites" from the left-side menu bar.
3. Click on the "Edit Site" button next to the website builder you want to use.
4. Click on the "Website Builder" option, followed by the "Pages" option on the left-hand tool bar.
5. Select the page you'd like to set the header background image on to open the page's settings.
6. You can upload an image under the "Header Background Image" section.
7. Click "Save" at the top of the page to save your changes.

Please note that this will only set the background for that page. Once you have uploaded your header background image, there are several background image options you can set. You can also adjust how the background image appears on your page.