When an internal auditor is asked to join a project team to help design controls in a software application, the most appropriate action is to advise the project team on how to develop effective controls. This advisory role ensures that the internal auditor provides expert guidance on control design without becoming directly responsible for implementation, maintaining their independence and objectivity. This approach allows the internal auditor to contribute valuable insights while ensuring that controls are properly integrated into the application.

IIA Standard 2120: Risk Management

IIA Practice Guide: Information Technology Controls