heroku rename

heroku apps:remane --app <old-project-name> <new-project-name>

First update the name for the heroku app on the heroku dashboard (on the heroku website)
Then do this on terminal (Make sure you're in the right repository)

$ git remote rm heroku (Remove the remote from git)
$ heroku git:remote -a <new app name> (Add it back with it's new name)

$ git remote rm heroku
$ heroku git:remote -a newname

$ heroku apps:rename newname
Renaming oldname to newname... done
http://newname.herokuapp.com/ | [email protected]:newname.git
Git remote heroku updated