According to the PMBOK Guide, a change request is a formal petition for change in a project. It's a document that explains what are the changes to be made and the main reasons why they should be implemented1.
Change requests can either be submitted by internal or external project stakeholders. When a project manager realizes that some operational project requirements were not captured in the project scope of work, they should issue a change request to include the additional scope, and track the completion of the work items. This is the best way to ensure that the project deliverables meet the customer's needs and expectations, and that the project scope is aligned with the project objectives. The other options are not the best actions to take in this situation. Issuing a change request to remove items from the scope of work and keep the project on schedule (option A) may compromise the quality and value of the project deliverables, and may result in customer dissatisfaction or rejection. Documenting the issue in the lessons learned document, and discussing this with the project sponsor (option C) may be helpful for future projects, but it does not address the current issue or resolve the gap in the project scope. Arranging to pass the cost to the operational area since the customer will benefit (option D) may create conflicts and resentment among the project stakeholders, and may violate the project budget and contract terms. References: PMBOK Guide, 6th edition, pages 115-116, 123-124.