There has been some variation here in the preposition and number for the phrase “into our hands”. Initially, Oliver Cowdery omitted this phrase when he copied the text from 𝓞 into 𝓟. Later, probably when he proofed 𝓟 against 𝓞, Oliver supralinearly inserted the phrase, which is extant in 𝓞. Yet for his correction in 𝓟, he initially wrote “into our hand” but then virtually immediately added the plural s. The entire supralinear “into our hands”, including the correcting s, is written with slightly heavier ink flow. For a list of other cases where Oliver wrote hand, perhaps only momentarily, rather than the correct hands, see under Alma 5:4. For two instances of “into the hands of the Lamanites”, Oliver Cowdery initially wrote “into the hand of the Lamanites” (see the discussion under Alma 52:10). Elsewhere the Book of Mormon text has 23 instances of the plural “into one’s hands” but none of the singular “into one’s hand”. We get similar results for “into the hand(s) of X”, with 31 instances in the text of the plural “into the hands of X” but only one instance of “into the hand of X” (namely, in 2 Nephi 8:23, which is a quote from the King James Bible).
In the 1920 LDS edition for Alma 57:12, the preposition into was changed to unto, probably accidentally since this change was not marked in the 1920 committee copy. In no other case of the prepositional phrase “into … hands” did the 1920 edition change into to unto.
Summary: Restore in Alma 57:12 the original reading “into our hands” (the extant reading in 𝓞 as well as the corrected reading in 𝓟).