PostgreSQL - Switching to PostgreSQL for Ruby on Rails in Cloud 9 on AWS

Working on a RoR application. Development is in Cloud 9 on AWS. Production is on Heroku. I’ve been doing the development to date with the default SQLite3 database and then have added PostgreSQL for the production environment. I have had a contractor do some SQL work which seems to work for the PostgreSQL instance on Heroku but doesn’t work with my development/testing environment with SQLite3.

Any suggestions on how to switch my database from SQLite3 to PostgreSQL on AWS Cloud 9? What code within the project would I need to change besides changing the production gem to 'PG'? Any other suggestions for a work around? Thank you.