The 1837 edition omitted the indefinite article a before chief judge. This omission was undoubtedly accidental. It was not marked by Joseph Smith in his editing of 𝓟 for the 1837 edition. Nearby the virtually identical expression has been left unchanged:
The Book of Mormon text always repeats the article, if one exists, before both chief judge
and governor in conjoined structures:
Thus the indefinite article a needs to be restored before chief judge in Helaman 1:5, making this passage specifically agree with Helaman 1:13 and, more generally, with usage elsewhere in the text.
Summary: Restore the indefinite article a before chief judge in Helaman 1:5; the a was accidentally deleted in the 1837 edition.