According to the PBA Guide, a project manager should use negotiation skills to resolve resource conflicts and obtain the best possible resources for the project. Negotiation involves communication, collaboration, and compromise among the stakeholders involved in the resource allocation. In this case, the project manager should contact the other project manager to request the resource, and try to reach a mutually acceptable agreement that balances the needs and priorities of both projects. This is preferable to asking the procurement department to supply a different resource, which may introduce additional costs, risks, and delays to the project. It is also preferable to changing the schedule according to the availability of the resource, which may affect the project scope, quality, and stakeholder expectations. Asking the sponsor to obtain the resource as originally planned may not be feasible or effective, as the sponsor may not have the authority or influence to resolve the resource conflict, and may perceive the project manager as unable to manage the project resources. References: = PBA Guide, Chapter 5: Planning the Business Analysis Approach, Section 5.2.3:
Negotiating for Resources, page 97. PMP Exam Content Outline, Domain II: Process, Task 4: Acquire and manage project resources, page 9.