MGN Migrated Windows Instance - Attached keypair not working

In MGN --> Individual Host --> Launch Template --> EC2 Launch Template --->Added a New Key pair for the Host. But while the Test instance is launched unable to login to the Host with the already given keypair. As of now, Host is not AD Integrated so need to login with the Key pair for windows. Any assistance please OR is it possible to create an IAM user and use that IAM user to login to migrated Windows host using SSM Fleet manager so that once that IAM user is used for the first time, will that user be created as part of local Admin group in Windows Host. Is this possible ?