how can i convince someone about something in a letter?
A lettre of conviction
Here is a model for the letter of conviction:
Full name of the person you write about, his title or position, and addresss.
Dear Name Surename,
Your greetings, Your full name and title. Your explanation (Tell what happened and the outcome/resolve). I am hoping for your kind consideration upon this matter. Thank you.
Your signature over your printed name (and title if it is necessary). Your address and contact number/email.