When manually entering a course grade, you must use the appropriate grade type for the Gradebook schema you have selected. For example, if the course is graded on a simple letter grade scale, you will only be able to enter the letters A, B, C, D, or F. If the course is graded on a standard letter grade scale, you will also be able to add + (plus sign) or - (minus sign) to the letter grade. If the course is graded on a Pass/Not pass scale, you will only be able to enter the letters P or N.
A numerical value for the override can be entered, however the value will be mapped to the letter grade scale. For example, if the letter grade scale is set so the minimum % for an A grade is 95, then entering a numerical value of 97 will be mapped to 95%.
Go to Gradebook.,
Select the Gradebook tool from the Tool Menu of your site.
In the Course Grades column, select the down arrow within the cell for the student's grade and choose Course Grade Override.
Enter override score and save.
Enter the new course grade to replace the autocalculated grade.