Install heroku by simply running the following in the command line (mac terminal).
brew install heroku/brew/heroku
Once the installation is complete you can login by:
heroku login
Then you can push your existing repo to heroku:
git push heroku master
If you get the following error:
fatal: 'heroku' does not appear to be a git repository fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists.
Then you are probably missing the link to your app in heroku. Add the Heroku Git URL by:
git remote add heroku "HerokuURL"
Replace
"HerokuURL"
with your app URL that you can find at Heroku > You App > Settings > Info.
Run push heroku command again and vola, the repo is deployed to Heroku.