Here in the original manuscript, Oliver Cowdery initially wrote the predicate “turned them about” after the when-clause. This predicate completes the original subject, the Lamanites, which precedes the when- clause. But virtually immediately, Oliver supralinearly inserted the repeated subject they in 𝓞 (there is no change in the level of ink flow for the pronoun they). Yet at some later time, Oliver crossed out both the insert mark and the supralinear they. The ink for the two crossouts is very much darker and heavier in flow. The ink is so distinctive that this correction does not look like it took place when Oliver read the text back to Joseph Smith; instead, it seems that here Oliver later decided to implement a grammatical change on his own. Perhaps the fact that he had earlier inserted the they made him think that this they was unnecessary. Later in this account of Zerahemnah’s invasion into Nephite territory, there are two more examples of the repeated subject, both following an intervening when-clause (as originally here in Alma 43:36):
Oliver did not remove these two instances of the repeated subject, the pronoun he. He probably did not notice them since he did not initially omit them when he took down Joseph’s dictation. Thus in these two cases, the repeated subject was allowed to stand in the manuscripts as well as in the 1830 edition; finally, in his editing for the 1837 edition, Joseph removed the repeated pronominal subject he in these two later instances. The critical text will restore these two instances of the repeated subject as well as the one here in Alma 43:36 for which the repeated subject was initially omitted but then virtually immediately added; its later deletion appears to be secondary. For further discussion of this structure, see under subject repetition in volume 3.
Summary: Restore the repeated subject, the pronoun they, in Alma 43:36; although initially omitted in 𝓞, the pronoun was almost immediately supplied by Oliver Cowdery; only later did he consciously decide to remove this instance of the repeated subject in 𝓞; he left unchanged two nearby instances of the same construction, in Alma 43:54 and Alma 44:19; Joseph Smith later removed these two instances of the repeated subject, but the critical text will restore them.