The original manuscript is extant here, and the not comes before himself, not after it (thus “and he shewed not himself unto them”). Oliver Cowdery, when copying into the printer’s manuscript, initially placed the not after himself, but then later (with somewhat heavier ink flow) he corrected the placement of the not (putting it before himself ). Oliver’s error may have been influenced by the word order that occurs at the end of the next manuscript line:
Later in verse 12 the text reverts to the word order where not precedes himself:
Either word order is possible, so in each case we follow the earliest reading, thus “and he shewed not himself unto them” in the middle of verse 7.
Summary: Maintain in the middle of Ether 12:7 the placement of the not before himself in “and he shewed not himself unto them”, the reading in 𝓞 and the corrected reading in 𝓟.