By default, your thumbnail will be the first work you uploaded. You can upload a new image to represent your Showroom. This is not the image at the top of your Showroom. It is only the image shown in the Showroom Directory. YOUR DIRECTORY THUMBNAIL IMAGE MUST BE OF YOUR ARTWORK. This is important for both you and our Showroom visitors. We want our visitors to have a sense of what is in your Showroom, along with the icons representing what is in your Showroom and the range of artwork prices.
You can change your thumbnail in Settings.