First, you posted to the Adobe stock forum and not the contributor forum. I will solve this for you.
Second: generative AI assets can be submitted as JPEG or as PNG, and as this, they are no different from other assets. If you submit as PNG, you need to have a transparent background. If your asset has no transparent background, you have to submit the asset as a high-quality JPEG file.
As you probably do not have a transparent background, you need to delete your assets and resubmit as JPEG. I recommend, you copy/paste first the keywords and titles, as they can't be retrieved after deleting. The delete link is somehow “hidden” in the lower end of the asset description.
