5 CFR § 1201.83 - Serving subpoenas.
(a) Any person who is at least 18 years of age and who is not a party to the appeal may serve a subpoena. The means prescribed by applicable state law are sufficient. The party who requested the subpoena, and to whom the subpoena has been issued, is responsible for serving the subpoena.
(b) A subpoena directed to an individual outside the territorial jurisdiction of any court of the United States may be served in the manner described by the Federal Rules of Civil Procedure for service of a subpoena in a foreign country.