Presumably the original key still exists? I think that without it, you won't be able to do anything except destroy the state file.
Assuming you do have the original key, you should be able to change the secrets provider key to refer to the key by ID instead of alias. There's more information here:
https://www.pulumi.com/docs/intro/concepts/secrets/#aws-key-management-service-kms
You can pass the key reference on the command line (
--secrets-provider
) or override the value in the Pulumi.yaml file (or is it in the Pulumi.<stack>.yaml file? I forget).