The first step for a project manager in this scenario is to inform the neighbor that all project documentation, including the initial project plans, has been approved. This action is in line with the best practices of project management, which emphasize transparency and communication with stakeholders. It is important to provide assurance that the project is proceeding according to the approved plans and specifications. If the neighbor's concerns persist, the project manager can then consider escalating the issue or requesting a formal complaint, but the initial response should be informative and aim to clarify any misunderstandings.
References: This response is based on the principles of stakeholder engagement and communication found in the PMBOKGuide and the Professional in Business Analysis (PBA) reference materials, which highlight the importance of addressing stakeholder concerns promptly and transparently123.