Amazon RDS for mysql with VPC for Heroku application

I am trying to connect my application on heroku with my amazon rds account.

So I created a DB instance which is not publicly accessible but I am not sure about the steps to create security group(VPC is default) and set it up with heroku addon.

I tried to search for similar questions such as Heroku instances in an Amazon VPC - Possible? but didn't found any solution

Thanks