Insert Image as Content Image and not as Image in the Text

I love the funktion with press button and get the entry, but i have a huge problem with the picture.
I need to edit the post again to set the “content image” again (sorry i dont know the word in german its Beitragsbild)
I would love to choose to set the found image as content image and not insert it just in the text like i can add keywords or new pictures with the button (bottom left) but there i need the URL he dont know the image he allready found because its not yet uploaded to the gallery