While Configuring IAM using CloudFormation, Stack creation failed with error "Resource of type 'AWS::IAM::Role' already exists"

As the error msg says, you have already the same role existing you are trying to create from your stack. This could be left from previous attempt or someone might have already deployed (the same?) template with a role using the same name.

If you want to create multiple instances of the same template including IAM roles, you should not define RoleName as there can not be 2 roles with identical names on one account. See https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-iam-role.html

RoleName

A name for the IAM role, up to 64 characters in length. For valid values, see the RoleName parameter for the CreateRole action > in the IAM User Guide. .. If you don't specify a name, AWS CloudFormation generates a unique physical ID and uses that ID for the role name.

And if you are following these instructions https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/custom-setup-orcl.html#custom-setup-orcl.cf.config-iam I believe someone has already created that stack (or manually did IAM roles) so you could try to skip the IAM creation part (or delete 3 items mentioned and retry).