According to the Professional in Business Analysis (PMI-PBA) Guide, a change request is a formal proposal to modify any document, deliverable, or baseline. A change request should be submitted when there is a need to change the approved scope, schedule, cost, quality, or any other aspect of the project. In this scenario, the project manager and the team have identified a potential design problem that requires a revision of the approved design. Therefore, the project manager should inform the client of the problem and follow the change request process to obtain the necessary approvals and update the project documents accordingly. This will ensure that the client is aware of the issue and its impact, and that the project is aligned with the client's expectations and requirements. Conducting a proof of concept, amending the design specifications, or passing them to the development team are actions that should be taken after the change request is approved, not before. References: (Professional in Business Analysis Reference Materials source and documents)
* Professional in Business Analysis (PMI-PBA) Guide, Chapter 6, Section 6.4.1.1
* A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Seventh Edition, Chapter 8, Section 8.2.2.1