Featured Image – Autogenerating in my Plugin

My plugin automatically creates posts with an uploaded stock image. How do I make it the featured image in the post creation process?

Despite much research I’m not quite understanding how to automate featured image. My plugin grabs an image, creates a post, and puts the image in the media directory where its referenced.

However I’d like to set it as a featured image for further benefits. But there is no straightforward way (that I’ve found) to assign the featured image/post thumbnail.

Just some good links are all I need. I can find my way from there.