As explained under 1 Nephi 3:2, Joseph Smith, in his editing for the 1837 edition, changed nearly half the instances of the phrase “in the which” in the Book of Mormon, usually by omitting the the. (Also see the discussion under the addendum for 1 Nephi 3:2 at the end of this part of volume 4.) Here in Ether 9:11 we have an instance where the related phrase “by the which means” was edited to “by which means” in the 1837 edition (and probably by Joseph, although in this case he did not mark the deletion of the the in 𝓟). This was the only instance of “by the which” in the original text, although in Ether 10–11 Joseph changed at least four, possibly five, instances of “in the which” to “by which” (for discussion, see under Ether 10:10 and Ether 11:15). Here in Ether 9:11, the original “by the which means” will be restored in the critical text.
Summary: Restore in Ether 9:11 the definite article the in the phrase “by the which means”, the reading of the earliest text.