Internal Auditor receives an information affecting the company interest from a whistleblower .How the internal auditor has to act on the information?

He needs to investigate it, gather evidence of its existence and effect on company. In the light of his investigation he will decide what action is needed i.e. report to audit committee

Company policy will probably demand that the auditor confirms the information and then reports it.

The internal auditor needs to investigate on the reliability of the information provided and take action as per the companies policy. The internal auditor should also inform his superiors about the information.

Agree with Kamran.

Do more investigation to confirm the information.