The client's requirement is to adjust the section rating manually which included in the summary section of the performance form. As of now the only rating which can be adjusted manually is the overall form rating.
Is there any idea to resolve this?
As I remember in the Performance Management guide it is mentioned that it is possible to change the overall rating of the goal and competency sections, as long as the summary section called Goal Competency Summary Section is configured, this section allows you to make changes to those ratings, but I don't think it is a solution for your case.
And remember that it is not possible to perform this action in the standard summary section of the system.