Is something like this fine?
To whom it may concern,
Explanation with regards to education section:
Kindly note that before I received an Invitation to Apply and submitted my Express Entry profile I had made a mistake in the Education section with regards to my Diploma (NCC Education). I had set the dates to dates when the first and last exams or assignments where done, according to the diploma transcripts, which were December and June respectively. This was amended post the Invitation to Apply to October 2010 and September 2011 respectively as this was the official duration of the course after it was confirmed with the educational institution I attended. This does not change my CRS scores.