The original manuscript is not extant for the first instance in this passage of the phrase “after their manner”, but the printer’s manuscript is. The 1830 typesetter accidentally misread the their as this. We find further support for “after their manner” in the same phraseology later on in the verse (“to offer up thanks after their manner”).
Summary: Restore in Alma 31:23 the original reading “after their manner” so that there are two occurrences of this prepositional phrase in the verse.