In this passage the 1874 RLDS edition changed the plural ﬂocks to the singular ﬂock, probably accidentally since for virtually all other references to ﬂocks in this narrative in Alma 17–19 regarding king Lamoni’s sheep, we have the plural ﬂocks in the earliest text (29 out of 30 cases). The only exception is in Alma 17:27, where 𝓟 reads ﬂock but the original text probably read ﬂocks. See the discussion under that passage. Here in Alma 18:3, the RLDS text has continued with the singular ﬂock, but the critical text will maintain the plural ﬂocks, the earliest reading.
Summary: Maintain the plural ﬂocks in Alma 18:3, the reading of the earliest textual sources.