Help me I have to write a letter to Atticus Finch pretending I am Tom Robinson and I have to thank him for rep?

Help me I'm reading To Kill a Mockingbird in my english cl and my teache told me that I have to write a letter to Atticus Finch pretending I am Tom Robinson and I have to thank him for representing me in the trial. So that means I have to put my self in Tom Robinson shoes and I have no idea how to write this letter! Please help me!!!!! This is homework for tomorrow.