The blended image can be exported as a PNG-file. This file can be uploaded at Canva and integrated into your book cover design. At the top right of their homepage, you select create a design, for which you need a free Canva account. In case the first part of designing your own background image is too hard, you can select one of the many free images that are available on Canva.
Canva offers many interesting features, such as effects that transform the background image. Next, several elements can be dragged and dropped as desired. The text elements and visual elements can be resized and changed easily. Upon completion, the cover design can be downloaded as a PNG-file. For this example, the blended image was used as the background and text and the circle shape has been added in Canva: