If you want to rename your heroku app use: heroku apps:rename new_name
Please replace "new_name" with the name you want to give your app. make sure you do not include any "https://" because this will give you an issue. simply replace new_name with your app name
e.g heroku apps:rename grapefruitblog
After doing this, heroku requires that you update git remotes for all other local checkouts of the app. you can do this by running this command: heroku git:remote -a new_name
Again, replace new_name with the name you previously put in
e.g heroku git:remote -a grapefruitblog