Any time before or after publishing the article you can add or change the cover image of the article. Very simple and easy steps. Lets discuss how.
If you are in a new article you just need to click on the upload cover image block it will open your system files from where you can upload your desired image by browsing your computer.
There is one more procedure if image is already upload then you need to remove the existing image first just by clicking on the delete button/ Bin button at the bottom middle of the existing cover. That will remove the existing cover Instantly.