Please delete the AWS managed keys

Hello.

There is no charge for an AWS managed key just by owning it in your AWS account.
Charges are incurred when using KMS keys.
In other words, your AWS account may have AWS services that use AWS managed keys.
I think that if I stopped using the AWS service that uses the KMS key, the KMS key fee would disappear.
https://docs.aws.amazon.com/kms/latest/developerguide/concepts.html#key-mgmt