Detailed Instructions. Inside Address — Enter the name and address of the financial institution.This guide is designed to teach you how to write a letter of instruction for heirs, or anyone else who may benefit from a little more direction. A letter of instruction is a cheat sheet for anyone involved in settling your affairs. Unlike a will, this letter has no legal authority. Have the bank officer fill out the Bank Information portion. A letter of instruction can complement an estate plan and provide your loved ones with additional details about your assets and wishes after death. Edit, sign, and share letter of instruction online. No need to install software, just go to DocHub, and sign up instantly and for free. A bank letter is an official document from your bank that provides important information about your business' official bank account.