A Team Member Identifies a Risk Which Is Not Listed

A team member identifies a risk which is not listed in risk register. If the risk materializes, then the project will be delayed by 6 months. What should the PMO do in this situation?

A) Immediately inform customer
B) Find out how the team member identified the risk, as all of them were identified during project planning
C) Prepare a risk mitigation plan
D) Analyze the risk
E) File a change control request