Okla. Stat. tit. 63, § 3101.6

A. An advance directive may be revoked in whole or in part at any time and in any manner by the declarant, without regard to the declarant's mental or physical condition. A revocation is effective upon communication to the attending physician or other health care provider by the declarant or a witness to the revocation. B. The attending physician or other health care provider shall make the revocation a part of the declarant's medical record.