Here Oliver Cowdery initially wrote “the more part of it” in the printer’s manuscript, but then he crossed out the definite article the and supralinearly inserted the indefinite article a. The level of ink flow is unchanged, so the correction appears immediate and based on the reading of the original manuscript (no longer extant for this part of the text). The use of the indefinite article in this context is rare in the Book of Mormon text (thus explaining Oliver Cowdery’s natural tendency to write “the more part”). But there is one more example in the text with the a: “for a more history part are written upon mine other plates” (2 Nephi 4:14). For a list of all instances of “more part(s)” in the text, see nearby under Helaman 6:21.
This passage in Helaman 6:32 does have a problem with the referent to the singular pronoun it. Its referent seems to be the preceding “all these iniquities”, which is plural. Of course, the it could be considered as referring to the Nephites’ general state of iniquity, as if the text read “all this iniquity” (even though it is very doubtful the original text actually read “all this iniquity” instead of “all these iniquities”). Emending the pronoun it here in this passage to them is not a viable option since the reader would then tend to interpret “a more part of them”, at least initially, as referring to “a more part of the Nephites” since the preceding text reads “all these iniquities did come unto them in the space of not many years”. If any emendation is to be done, probably the plural “all these iniquities” should be changed to the singular “all this iniquity”. But as already observed in other passages, there is considerable switching in grammatical number in statements where either the singular or the plural will work semantically. See, for instance, the discussion regarding it and them under 1 Nephi 19:24, where in the original text the singular pronoun it refers to an earlier plural, “the words of the prophet”. The critical text will maintain the singular it here in Helaman 6:32 even though it refers to a plural, “all these iniquities”.
Summary: Accept in Helaman 6:32 the indefinite article a in “a more part of it” (the corrected reading in 𝓟); also retain the singular pronoun it even though its antecedent is the plural “all these iniquities”.