Neb. Rev. Stat. § 20-406

(1) A declarant may revoke a declaration at any time and in any manner without regard to the declarant's mental or physical condition. A revocation shall be effective upon its communication to the attending physician or other health care provider by the declarant or a witness to the revocation. (2) The attending physician or other health care provider shall make the revocation a part of the declarant's medical record.