Apple Book - not showing back cover artwork

Hi all - I recently update the cover art for my self published book. I've been able to update the front cover no problems. Previously I could add a screen shot of the back cover artwork but can't locate now how to do this nor can I remove the old back cover artwork.

Screen shot showing new front cover but old back cover. So when you find the book in the store, it shows new front cover, old back cover. The Book location is here.

Any suggestions please?