As explained under 1 Nephi 22:4, Oliver Cowdery frequently mixed up whether and whither in the manuscripts. Here in Helaman 6:8, he wrote the impossible whethersoever in the printer’s manuscript, probably because he was influenced by the two instances of whether elsewhere in this passage. The 1830 compositor correctly set the word as whithersoever since the clause refers to motion (“the Lamanites did also go whithersoever they would”). In fact, the word whithersoever corresponds to the phrase “into whatsoever part of the land”, found in the preceding verse:
Summary: Maintain in Helaman 6:8 the form whithersoever, not the impossible whethersoever that Oliver Cowdery wrote in 𝓟.