Here the 1837 edition removed the redundant he. As already discussed under Mosiah 8:7, in the original Book of Mormon text the subject is frequently repeated as a pronoun when there is an intervening participial clause. Some of these redundancies have been removed, as here in Mosiah 21:23, but others have been left unchanged. For further discussion and a complete list of examples, see subject repetition in volume 3.
Summary: Restore the repeated subject he in Mosiah 21:23; such usage was fairly common in the original text and is still found to some degree in the current text.