The original manuscript is extant here for the two instances of the plural lands: a direct object “our lands” followed by an appositive noun phrase, “the lands of our first inheritance”. When Oliver Cowdery copied the text from 𝓞 into 𝓟, he changed the first lands to land, giving “our land / the lands of our first inheritance”. In the 1837 edition, the first part of the appositive noun phrase was omitted, giving “our land of our first inheritance”, a rather awkward expression. The deletion of the lands was probably accidental (especially since Joseph Smith didn’t mark it in 𝓟). The 1908 RLDS edition restored the reading of 𝓟 and the 1830 edition (“our land / the lands of our first inheritance”). The 1920 LDS edition made a similar restoration except that the plural lands in the appositive was replaced by the singular land, so as to make the two nouns agree in number, thus “our land / the land of our first inheritance”. (The editors for the 1920 edition made a similar emendation nearby in Alma 54:6, changing “or the lands of your possessions” to “or the land of your possessions”.) Here in Alma 54:13, the critical text will, of course, restore the original text, with the two nouns agreeing in the plural: “our lands / the lands of our first inheritance”.
The plural phrase “lands of one’s inheritance” occurs fairly often in the text, usually in reference to the house of Israel or to the Jews (see the discussion under 2 Nephi 9:2 for examples). There are also examples of this plural phrase referring to the Nephite lands in general (in the Words of Mormon 1:14 and in Mormon 2:27–28). We also find examples of the related phrase “lands for one’s inheritance” in reference to the Zoramite converts (in Alma 35:9, 14) and to the people of Ammon (in Alma 43:12). Thus the original plural lands in Alma 54:13 is perfectly acceptable.
Summary: Restore the plural lands both times in Alma 54:13, the reading in the original manuscript (“we will seek our lands / the lands of our first inheritance”).