I was making the git push for the other's repository to my private one. And then I got this error.
The simple solution was deleting the upstream and main and just publish it as a new one through the Visual Studio Code.
Viewing and Deleting Codes look like this.
$ git remote -v
origin https://github.com/BYUCS260/learning-mongo.git (fetch)
origin https://github.com/BYUCS260/learning-mongo.git (push)
upstream https://github.com/BYU-CS-260-Winter-2019/learning-mongo.git (fetch)
upstream https://github.com/BYU-CS-260-Winter-2019/learning-mongo.git (push)
$ git remote remove upstream
$ git remote remove origin
$ git remote -v
//nothing
//Then just publish the page to GitHub through using VS Code
https://www.cloudbees.com/blog/remote-origin-already-exists-error