Um... where do I get a book cover 
Book cover
You can try your luck at these threads but don't forget that you are not entitled to a free cover. The artists do it for practice/fun so they get to decide if they want to do it or not. Also don't forget to read the first post of the threads to learn their rules. Good luck!
https://forum.webnovel.com/d/9818-free-covers-for-your-stories
https://forum.webnovel.com/d/11331-free-covers-for-your-stories