It sounds as if you need to run ansible on an AWS instance, and create an instance policy for the instance. Read up on instance policies in the AWS doco.
The simplest instance policy is just a role that gives the instance AdministratorAccess, but depending on what you are planning to use Ansible to do, that may be overkill. You should avoid giving an instance too much power, just as you should avoid giving a user too much power.
The big advantage of using an instance policy is that software on the instance - like Ansible - can do anything the instance is allowed to do, without having to worry about IAM users, access keys or secrets of any kind (although you will need to be able to log into the instance to do stuff).
The other thing you can do is attach a limited instance policy first, and change it later - any change to the role will be effective almost immediately.
Regards, K.