Role is not attaching or available for use after creation for Container Services

For container instances to receive the new ARN and resource ID format, the root user needs to opt in for the container instance IAM role.

I've made a role that should have the right permissions, but** I can't find how to attach it to admin/root.** Step 10 here - The formatting doesn't work in both PowerShell and CLI.

The role is made, but it's also** not showing up in the drop down under** 'Container instance IAM role'.