The 1858 Wright edition replaced the determiner this with the. The first two RLDS editions also followed this reading, but the original reading was restored in the third RLDS edition (1908), probably by reference to the printer’s manuscript. The change may have been an attempt, perhaps unconscious, to avoid a sequence of demonstrative pronouns close together (“these plates … this small account … this king Benjamin”). The critical text will maintain the earliest reading, “this small account”.
Summary: Retain the demonstrative this in the Words of Mormon 1:3 (“this small account”).