Instructions for completing the necessary forms are included at the end of this packet. You don't need to write any letter, additionally, no one would entertain withdrawal on the basis of a letter, the mandate should be clear.Contact your bank for a power of attorney form. How do I set up direct deposit? To set up direct deposit (ACH) to your account at Fifth Third Bank, you can fill out a Direct Deposit Authorization form here. Use this letter to tell a company that you are taking away your permission for the company to take automatic payments out of your bank account.