- Expose your RDS instance to outside world.
- Use pgloader to copy over your MySQL db to a local Postgres instance on your development machine.
- Dump your local Postgres db.
- Use
heroku pg:backups:restore
to upload your Postgres db dump.
- Follow the basic instructions for preparing your AWS RDS instance for data export (https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/MySQL.Procedural.Exporting.NonRDSRepl.html). The most important part is to make sure that you have all your security settings (e.g., VPC, subnet, db security group if applicable) set up to expose port 3306 to the outside world and have your db root username and password. If you've forgotten your db's root password, follow these instructions to reset it: https://aws.amazon.com/premiumsupport/knowledge-center/reset-master-user-password-rds/