According to the PMBOK Guide, 7th edition, section 13.1.1, "Stakeholder identification is the process of identifying the people, groups, or organizations that could impact or be impacted by a decision, activity, or outcome of the project, and analyzing and documenting relevant information regarding their interests, involvement, interdependencies, influence, and potential impact on project success." Therefore, the project manager should conduct stakeholder identification and a project objectives review session, as this will help to ensure that the new key stakeholder is properly engaged and informed about the project scope and deliverables. Creating a change request and updating the scope management plan (option A) may not be necessary or appropriate, as the issue may not be related to the scope, but to the stakeholder's expectations or understanding. Updating the stakeholder list and fixing the deliverables (option C) may not address the root cause of the issue, and may introduce unnecessary changes or rework. Updating the project management plan and lessons learned (option D) may be done later, after the issue is resolved and the stakeholder is satisfied.
References:
* PMBOK Guide, 7th edition, section 13.1.1
* PMI-PBA Exam Practice Test and Study Guide, 2nd edition, page 180, question 14