The original manuscript is extant here and clearly shows the then, but there is no &. While copying into the printer’s manuscript, Oliver Cowdery initially wrote an ampersand; then he immediately overwrote the & with a t and followed inline with the rest of the word then. But the 1830 typesetter set And then, which has continued throughout all subsequent printed editions.
The question here is whether then needs to have an immediately preceding and. Elsewhere in the text, there are 14 examples where then heads a sentence-initial clause containing the main verb say, as in the following example:
And there are also five cases where the and then heads a sentence-initial clause containing say, as in this example:
So either transition is possible. Therefore, here in Alma 30:36–37, the transition without the and (as specified in the two manuscripts) will be followed.
Summary: Restore in Alma 30:37 the reading of the two manuscripts, namely, the then without a preceding and.