Oliver Cowdery initially wrote feel in the original manuscript; then somewhat later he corrected feel to fear (the supralinear fear was written with heavier ink flow). This correction probably occurred when Oliver read back the text to Joseph Smith. He probably misheard Joseph’s fear as feel, two phonetically similar words (identical except for the final liquid, /r/ versus /l/).
Usage elsewhere in the text favors fear that; there are 13 other occurrences of fear complemented by a that-clause, including one earlier in this chapter: “fearing that we should cut them off from their support” (Alma 58:15). There are no instances in the text of feel complemented by a that-clause; nonetheless, such an expression is not impossible since there are instances of feel with other types of complements:
Here in Alma 58:36, the verb fear seems to better express Helaman’s uncertainty about what was actually happening in the land of Zarahemla. The critical text will accept Oliver Cowdery’s corrected reading in 𝓞, fear (“behold we fear that there is some faction in the government”).
Summary: Accept in Alma 58:36 Oliver Cowdery’s correction of feel to fear; he probably misheard Joseph Smith’s fear as feel.