The program manager should first obtain details from the owner of the project that is causing the delay, such as the root cause, the impact, the mitigation plan, and the revised timeline. This will help the program manager to assess the situation, communicate with the stakeholders, and adjust the program schedule accordingly.
Updating the critical path, applying contingency reserves, and reestimating epic user stories are possible actions that the program manager may take after obtaining the details, depending on the severity and duration of the delay. However, they are not the immediate next steps, as they require more information and analysis.
References = CompTIA Project+ Study Guide: Exam PK0-005, Third Edition, Chapter 10: Executing the Project, page 2431; Dealing with delays - Project Management Institute2