As discussed under 2 Nephi 11:3, the word also can appear right before the perfect auxiliary have. Here in Jacob 7:12, the 1906 LDS edition accidentally shifted the also to after the perfect auxiliary. Both word orders are found in the original text, so in each case we follow the earliest textual sources in determining the correct order.
The 1837 edition here changed the perfect auxiliary hath to has. For further discussion of this kind of editing, see under infl al endings in volume 3.
Summary: Maintain in Jacob 7:12 the original word order in “it also hath been made manifest”.