Mo. Rev. Stat. § 81.013
If the charter of a city or town under special charter provides for amendment of the charter only by act of the general assembly of the state of Missouri or does not provide for amendment of the charter, the charter may be amended if a proposition to amend the charter is submitted to a vote of the qualified electors of the city or town and a majority of the qualified voters voting on the proposition vote in favor thereof. A proposition to amend the charter may be submitted to the qualified voters of the city or town at the next municipal election, or at a special election called for the purpose, by an ordinance adopted by the chief legislative body of the city or town; and a proposition to amend the charter shall be so submitted if a petition so to do signed by ten percent of the qualified voters of the city or town, as determined by the total number of votes cast in the city or town for governor at the last preceding gubernatorial election, is presented to the body or official in charge of municipal elections of the city or town.
§ 81.013, RSMo