Oliver Cowdery wrote in the printer’s manuscript “and turn the Lord their God”, which clearly makes no sense. Later Oliver inserted the word unto here. His insertion is in pencil, which suggests that he did the correction in the printer’s shop and without reference to the original manuscript. For two other nearby examples where Oliver edited the text while apparently in the printer’s shop, see the change of save to serve in Mosiah 4:14 and chance to change in Mosiah 5:2, also both in pencil. But in Mosiah 11:23, the emendation is not quite as obvious as in the two other examples; here his emendation could have been wrong since another obvious possibility is that the preposition was to rather than unto. Elsewhere in the Book of Mormon, there are 11 other occurrences of “turn (un)to ”:
The current text has one additional example of “turn (un)to ”, but it appears that this example originally read return rather than turn:
See under that passage for further discussion.
We should also note that for this phrase the King James Bible uses both prepositions with approximately the same frequency; there are 13 of “turn to ” and 16 of “turn unto ”, including the following contrastive pairs:
The variation in the King James text is essentially random, but this does not seem to be the case in the Book of Mormon text. When we consider the distribution of to and unto in the Book of Mormon for “turn (un)to ”, we find that everywhere else in the books of Mosiah and Alma, the preposition is to, while unto is found only later in the text and in one biblical citation (2 Nephi 19:13, which quotes Isaiah 9:13). Note in particular that Mosiah 11:21, only two verses away from Mosiah 11:23, reads to; in fact, the language is virtually identical: “except they repent and turn to the Lord their God”. Since the evidence suggests that Oliver’s emendation was done in the printer’s shop and without consulting 𝓞, we can conclude that the emendation in verse 23 represents only his guess. Given that all nearby passages read to, the more likely emendation here in Mosiah 11:23 is to. The critical text will therefore emend unto to read to (“except this people repent and turn to the Lord their God”).
Summary: Replace unto, Oliver Cowdery’s conjectural emendation in Mosiah 11:23, with to; usage elsewhere in Mosiah and Alma, including the nearby case in Mosiah 11:21, suggests that to is more likely than unto as the original reading for this passage.