When you add a promotion to a tab on your Facebook page you have option to customize the full content around your entry form. Add images, content, links and any other HTML elements that you would like to provide your users with an experience consistent with your brand. This option is available for Business and Brands & Agencies accounts.
After you’ve published your campaign you can click on the ‘edit your hosted page’s layout‘. This will open a layer with your entry form’s code. Before or after this code you can enter any HTML that you would like.
After you’ve updated and saved the content of this hosted page check the box under ‘Add your entry form to Facebook pages‘ to enable the ‘Use customized Hosted Entry Form Page in Facebook page tab’ and click Save. Done! Your new design will immediately begin appearing as the content with the tab on your Facebook page.