Here in the original manuscript, Oliver Cowdery initially wrote Jershon as Jershur, then virtually immediately corrected Jershur to Jershon by overwriting the final ur with on. There is no change in the level of ink flow for this correction.
This is the only place in extant portions of 𝓞 where the name Jershon was ever misspelled or miswritten. (In the printer’s manuscript, Oliver Cowdery once miswrote it as Jeshon, in Alma 28:1.) The first occurrence of the name Jershon is extant in 𝓞 and is found a little earlier here in Alma 27:22: “we will give up the land of Jershon”. Perhaps for the second occurrence of the name, initially misspelled as Jershur, the final ur was influenced by the preceding er in the name (especially since the er was likely pronounced /t/ rather than /er/). It seems less likely that Oliver was affected by the biblical place-name Geshur, the land where Absalom lived in exile (referred to in 2 Samuel 3 and 2 Samuel 13–15 as well as in 1 Chronicles 2–3), although we cannot wholly discount such an influence since Oliver seems to have been influenced by biblical names elsewhere in this part of the text (see the discussion regarding Amalekites and Midian under Alma 24:5). In any event, Jershon is definitely correct.
Summary: Maintain the name Jershon in Alma 27:22 and elsewhere in the text; the first occurrence of the name is extant in 𝓞 and reads Jershon.