Okla. Stat. tit. 6, § 2021

A credit union chartered under the laws of the State of Oklahoma may be converted to a state credit union under the laws of any other state, or to a federal credit union either within or without the State of Oklahoma. A credit union chartered under the laws of the United States or any other state may convert to a credit union under the laws of the State of Oklahoma. To effect such a conversion a credit union must comply with all requirements of the authority under which it was originally chartered and the requirements of the State Credit Union Board and file proof of such compliance with the State Credit Union Board.