You cannot change any grades for a student that has a concluded enrollment. All students’ Sem 1 enrollments were concluded the first day of the 2nd semester.
How to Restore a student’s enrollment:
Go to the Course
Click the Gear icon in the top right
Select View Prior Enrollments
Click student’s Name
Click More User Details…
Click Restore this Enrollment
If you change a grade within Canvas after grades have been exported into Infinite Campus, then you must give the student's new Final Grade to the office manually.