Here in Ether 7:13 Oliver Cowdery initially omitted the indefinite quantifier many in 𝓟. 𝓞 is not extant here, but it seems reasonable that many was in 𝓞 since either reading, with or without the many, is possible. In addition, the ink level for the supralinearly inserted many is unchanged, which implies that the correction in 𝓟 was virtually immediate. For two other examples where many was omitted in the text (one is conjectured), see under 3 Nephi 21:9. Here in Ether 7:13 the critical text will follow the corrected reading in 𝓟.
Elsewhere the text does not use many when referring to people repenting (or not repenting) of their sins, iniquities, or evil doings. There are 40 instances of “repent of one’s sins, iniquities, or evil doings”; there are also 7 instances of “repent of all one’s sins or iniquities” (that is, with the universal quantifier all ). But only here in Ether 7:13 do we have an instance where this expression has many. The unexpectedness of the many is probably the reason why Oliver Cowdery omitted it initially here.
Summary: Maintain in Ether 7:13 the occurrence of many, the corrected reading in 𝓟; there would have been no motivation for Oliver Cowdery to have added many here unless it was in 𝓞.