Normally, when I deploy to Heroku, I create the heroku app from within the Rails console with the command
heroku create mycustomappname
and then it creates that heroku url
http://mycustomappname.herokuapp.com
and then when I push to heroku, the app is available at that custom domain.
However, after creating a canvas app on Facebook, and selecting Heroku to host, Facebook gave me the heroku url. I have a rails app on my local host. How do I push to that specific heroku url if it wasn't created from within the Rails console?