pgwp letter of explanation

[tall_vish]

I am in need of some advice on how to type up a letter of explanation, I had to redo a class in the last semester of my program last year (Summer 2021 term). The class, however, resumed only on winter and summer semesters so between September to December last year, I had to take a break and redo the class this year. I have finally graduated but now am told should write up a letter to explain the situation. How should I go about this? Is there a reliable site to source a sample from? I understand that I can be a part time student in the last semester but breaks are now allowed without reasonable explanation.