The word now is supralinearly inserted in both manuscripts, and in each case with heavier ink flow. In fact, the now in the original manuscript was written with an extremely heavy ink flow, so it seems very unlikely that Oliver Cowdery would have initially missed the word when he first copied this passage into 𝓟—unless 𝓞 didn’t have the now at that time. To be sure, the text would have read rather awkwardly here without any transitional word before Moroni. Under that assumption, it seems quite plausible that Oliver edited the text here by supralinearly inserting the now, first in 𝓟, then correcting 𝓞 to agree with 𝓟.
There are actually three supralinear corrections for this line in 𝓟. One was virtually immediate, namely, the correction of where to whether, discussed above. There is no change in the level of ink flow for this correction, nor is there any change in the sharpness of the quill. In contrast, the two other supralinear corrections are written with heavier ink flow, namely, the restoration of the present participial phrase “being much confused” (which is extant and written inline in 𝓞) and the secondary now. Moreover, the heavier ink flow for these two corrections in 𝓟 is identical, the quill used to write them was equally dull, and they were both inserted above the supralinear correction of where to whether:
It is quite clear that the now was inserted in 𝓟 at the same time Oliver Cowdery restored the present participial phrase “being much confused”. In other words, Oliver decided to insert the extra now into the text when he proofed 𝓟 against 𝓞, considerably later than when he first copied the text from 𝓞 into 𝓟. Moreover, the supralinearly inserted now in 𝓞 appears to have been written using the same dull quill used to make the correction in 𝓟.
Ultimately, the question is whether any emendation was necessary here in Alma 52:37. Earlier in this passage, we have a similar example that does not have any transitional word at the beginning of its verse (marked below with an arrow):
The participial clause at the beginning of verse 34 means ‘since Moroni was in their course of march’. Similarly, we can interpret the participial clause at the beginning of verse 37 as meaning ‘since Moroni saw their confusion’. Just as in verse 34, the extra now in verse 37 is not necessary. The critical text will therefore remove this secondary now from Alma 52:37.
Summary: Remove from Alma 52:37 the intrusive now that Oliver Cowdery added later to both manuscripts when he proofed 𝓟 against 𝓞; although unusual, the original sentence-initial present participial clause (“Moroni seeing their confusion”) is acceptable without any now, just as the one at the beginning of Alma 52:34 is acceptable (“Moroni being in their course of march”).