How to create a secondary db in a Postgres Instance in AWS

I have a TF that creates a Postgres DB in Amazon. This instance has a initial db

resource "aws_db_instance" "main" {
  identifier                  = "${var.role}-${var.environment}"
  instance_class              = var.rds_type
  allocated_storage           = var.db_storage_size
  multi_az                    = var.multi_az
  storage_type                = "gp2"
  engine                      = "postgres"
  engine_version              = "12.6"
  name                        = "mydb"
  username                    = "username"
  password                    = random_password.password.result

But I need to create a secondary Db inside the same instance. Do you know how to achieve that?
I found this example (for mysql) in the web where it says that this will do it

# Create a second database, in addition to the "initial_db" created
# by the aws_db_instance resource above.
resource "mysql_database" "app" {
  name = "another_db"

is ther anything similar for Postgres?
Any help would be appreciated.