Here the 1911 LDS edition accidentally replaced the preposition unto with to, which is what we expect in modern English. The 1920 LDS edition restored the original unto. Note that the following sentence also has unto, not to (“and he did expound all things unto them”). For additional discussion regarding unto versus to, see under 1 Nephi 3:23.
Summary: Maintain in 3 Nephi 26:1 both instances of the preposition unto, the reading of the earliest sources.