If anyone has a sample letter of explanation, please pass on to me. I know its optional but i believe its good to put in some effort in to that letter.
everyone's letter would be different. its to explain any inconsistencies, anything you're missing, anything you want to give further information on about YOUR profile. there's no template. its specific to what you're submitting.
Instead, I have just written like a paragraph.
It is always better you write in a letter format and as purplesnow mentioned the content and format can vary.