Overview

When trying to approve a Change Manager template for a Fixer and if it doesn't have a Template Approver, then the below warning is seen:

There are NO Template Approvers for this Fixer. Please add at least one Template IAM Approver
before proceeding with Change Manager template approval.

Solution

Click Add Template Approvers in the above screenshot and it will bring up a dialog to add the approver:

The user being entered in the AWS IAM user ID field should exist in your AWS account.

If you try to add an user that doesn't exist in your AWS account, then a No such user: <user's name> error will be seen.