Cloud9 MERN app development Help

Cloud9 has been a great tool to use to practice web dev anywhere I go. I’ve been struggling getting a full stack app to work with Cloud9, probably because I haven’t gone into the config details deep enough.
The simplest thing I want to do is deploy an express backend on Heroku with CORS enabled, and then develop with a create-react-app based frontend making simple fetch requests to the API. Been struggling with getting the React app to work with the proxy specified as my Express server hosted on a diff. port on Cloud9 in the same workspace.
Essentially if someone can show how to get this app working in cloud9 I can work through how to make it work for my app. Thank you!

And of course if someone needs further explanation I can gladly give more details