Here in the 1840 edition, an extra may was inserted into the text. This intrusive modal has been retained throughout the RLDS textual tradition. The addition of this word to the text was probably accidental and not the result of Joseph Smith’s editing for the 1840 edition. It was most likely added because of the use of the modal may throughout this passage. Yet may is actually restricted to the main clauses in this passage, while its subordinate when-clauses never have the may:
The critical text will therefore maintain the earliest reading without the intrusive may in clause number 2.
Summary: Reject the intrusive may in the second when-clause of Helaman 5:6, first introduced in the 1840 edition (most likely as a typo by the 1840 typesetter).