Is it possible to remove a custom option group from RDS in AWS?

From the document, it can be deleted if it’s not associated to any snapshot or db instance.

But now due to an aws provider version upgrade for terraform, the AWS RDS Terraform module changes something for option group in AWS.

It added a new one and want to delete the old one. The old one is using and is associating with many snapshots so can’t been deleted.
After finish run the terraform apply, check AWS found both the new one and old one exist. On the DB instance modify page found the default selected option group is the new one.

Now use terraform, can’t find a way to remove one of them. And the task always tried to delete the old option group(how to avoid it?).

For the current situation, is it possible to delete the new option group from AWS?

I found this question, it said custom option group defined in Terraform. But I didn’t found which key name it is.

When upgrade the aws provider version from Terraform, the db operation was used module

module "db" {
  source  = "terraform-aws-modules/rds/aws"
  version = "~> 2.0"


Where can remove the custom option group by Terraform?