The header/banner of a website is the first thing your visitors see when they visit the website. Therefore, it is important that the header is specialized to the visitors' viewing the website. It is also possible to set a different header for each of your clones. This is ideal if, for example, you want to emphasize the best-selling products of that country in the header, or have an image related to a country in your header. A header can be an image, but also a slideshow of multiple images.
To change the header you need to inspect it (using right mouse click), and copy the corresponding script from the banner. In Clonable you past this into the left column. In the right column you paste the exact code, but now change the filename of the existing image into the filename of the new image. That piece of code looks like a URL.
Make sure you copy the whole piece of code to prevent making unwanted changes in scripts.