Scribe 2 of 𝓟 started to write “thus retained a remission of sins”. He had just started to write the final d of retained when he aborted it, redipped his quill (thus increasing somewhat the ink flow for the subsequent correction), overwrote the d with in, and then continued inline writing the final g before going on with “a remission of their sins” (also inline). The initial retained was probably an unintended scribal slip and was therefore immediately corrected. The surrounding text also has present participial verb phrases, looking forward and being filled, which supports the corrected reading “thus retaining a remission of their sins”. The critical text will, of course, accept the corrected reading in 𝓟.
Summary: Accept in Alma 4:14 scribe 2’s immediate correction in 𝓟 of retained to retaining; the surrounding use of the present participles looking and being support retaining.