What is the process to update vault aws role backend policy of type `iam_user`

We have configured a vault aws secret backend with an iam_user role.
We have to update to attached policy to the role.
For that we use terraform ressource.

The terraform update well the vault role. but the aws iam_user policy is not updated on AWS.

What is the process?
We have trying to revoke all lease but it not update or drop/create the iam_user.
We ended by deleting the iam_useron AWS and waiting vault to recreate it. but it’s too long.

Thanks for your help