Here Oliver Cowdery initially omitted the subject pronoun he. He later supplied the he supralinearly, perhaps when he proofed 𝓟 against 𝓞 (the change in the level of ink flow is slightly heavier). Nearby, in verse 3 of this chapter, Oliver made the same error. In that case, he corrected his error virtually immediately since there is no difference in the level of ink flow for the supralinear he:
Since either reading—with or without the he —will work in Ether 14:17, the critical text will follow the corrected reading. Oliver’s only motivation here would have been to make sure that 𝓟 read as it did in 𝓞.
Summary: Accept Oliver Cowdery’s correction in Ether 14:17 (namely, when he supplied the subject pronoun he, presumably when he proofed 𝓟 against 𝓞).