A letter of instruction is an important document used to help navigate the process of estate planning. Otherwise known as a letter of intent.These instructions are designed to help you complete the Trustee Certification of Trust for a Line of Credit. Probate Court handles cases involving the property of deceased persons, wills, trusts, guardianships and conservatorships. 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 document that guides a designated individual or entity on how to carry out specific actions or wishes after the author's demise. Before you complete Form. M2, complete federal. Support Letter, the Directing Holders directed the Trustee to, among other things, submit the. A letter of instruction, or letter of intent, is a simple document that can take the guesswork and headache out of settling your estate.