When creating a new story, you'll see a pre-selected color as a banner. To change the banner, first click on it, then select the '...' and select either 'edit' or 'remove'.

If you click on 'edit', you'll be able to either select one of our templates or upload your own image. If you upload your own, the recommended dimensions are 1920x400px or higher.

If you remove a banner, you can get it back as on the screenshot below: