In case an employee has grievance after calibration

Summary:

Scenario: After the performance document is shared by the line manager with the employee, the employee shows concern about his rating and appeals. i.e. Employee shows grievance that the manager has been unfair.

Prior to line manager sharing the document, the calibration happens offline and the overall/manager rating will be uploaded on the document using hdl this will become the final overall rating.

How to handle this in performance document while the document is finally shared to employee? Is there any hdl or spreadsheet loader (if yes, please share) to modify the overall/manager ratings by HR Specialist ?