Here Oliver Cowdery initially wrote the singular hand in 𝓟; but then virtually immediately he inserted the plural s inline (there is no change in the level of ink flow). Although 𝓞 is not extant here, it undoubtedly read in the plural. As discussed under Alma 52:10, the Book of Mormon text always uses the plural hands in the expression “fall into the hand(s) of X”.
Summary: Accept Oliver Cowdery’s virtually immediate correction from hand to hands in Helaman 4:9; the text consistently uses the plural hands in the expression “fall into the hand(s) of X”.