Here the 1905 LDS edition replaced the demonstrative determiner that with the definite article the. The current LDS text continues this reading (“in the great and last day”). This change appears to be accidental. As discussed under 2 Nephi 33:12, there are examples in the original text of both “that great and last day” and “the great and last day”. In each case, the critical text will follow the reading of the earliest textual sources, thus restoring here in Helaman 12:25 the demonstrative that.
Summary: Restore the demonstrative that in Helaman 12:25: “in that great and last day”.