The ISO 3166 Maintenance Agency makes the changes to ISO 3166. They follow notifications from and include members from these other bodies:
Association française de normalisation (AFNOR), France
American National Standards Institute (ANSI), United States
British Standards Institution (BSI), United Kingdom
Deutsches Institut für Normung (DIN), Germany
Institut Marocain de Normalisation (IMANOR)
Iran National Standards Organization (INSO)
Standards Australia (SA)
Standards Council of Canada (SCC)
Swedish Standards Institute (SIS)
International Atomic Energy Agency (IAEA)
International Civil Aviation Organization (ICAO)
International Telecommunication Union (ITU)
Internet Corporation for Assigned Names and Numbers (ICANN)
Universal Postal Union (UPU)
United Nations Economic Commission for Europe (UNECE)
https://www.iso.org/iso-3166-country-codes.html