N.Y. Gen. Oblig. Law § 5-1554
A parent may revoke a designation by notifying, either orally or in writing, the designee or a school, health care provider, or health plan to which the designation has been presented, or by any other act evidencing a specific intent to revoke the designation. A designation shall also be revoked upon the execution by the parent of a subsequent designation. Revocation by one parent authorized to execute such a designation shall be deemed effective and complete revocation of a designation pursuant to this title. A designee who receives notification from a parent of any such revocation shall forthwith notify any school, health care provider or health plan to which a designation pursuant to this title has been presented. A parent may directly notify any such school, health care provider or health plan of the revocation, in which case the failure of the designee to notify such entities of the revocation shall not make revocation ineffective.
N.Y. Gen. Oblig. Law § 5-1554