Follow this simple steps:
You will find this option in WordPress Dashboard -> AMP option panel -> Advanced Settings -> Enable “Featured Image from the Content” option and click on the “Save changes” button.

Scroll down a little to see this option

- Featured Image from the Content: Show the first image of the content as Featured Image if there is no featured image.
That’s it for this tutorial!
We hope it helped you. If you have any feedback or questions, then please share them in the comments section below.