As explained under Alma 46:24, the critical text will restore all instances of the double genitive “X of Y’s” whenever there is support for it in the earliest textual sources (in all there are four instances, including this one in Helaman 1:25). For this passage, in both 𝓞 and 𝓟 the text reads “this march of Coriantumr’s”, which is how the critical text will read. (Oliver Cowdery did not supply the apostrophe in either manuscript for the singular possessive Coriantumr’s. Oliver’s general practice in the manuscripts was to omit the apostrophe, as explained for the phrase “three days’ journey” in the discussion under the 1 Nephi preface.) Here in Helaman 1:25, the 1830 typesetter decided to remove the possessive s, giving “this march of Coriantumr” (the reading of all the printed editions).
Summary: Restore the singular possessive form Coriantumr’s in Helaman 1:25, the reading in both manuscripts (although written there without the apostrophe, in accord with Oliver Cowdery’s scribal practice); this use of the double genitive is supported by three other instances of that usage in the original text.