Chabad.org — English translation + Rashi
Torah Temimah points to Toras Kohanim (Sifra), Vayikra Dibbura DeChovah, on 4:26 (ve-chipper alav — one person, kohen himself) (unit 5; single primary locus per emergency Core plan).
Sefaria — Sifra / Toras Kohanim, Vayikra Dibbura DeChovah
English: “And he shall atone for him” — “for him” teaches that he does not atone for two at once, and that the kohen atones by his own hand.
One person; kohen performs the avodah — kapparah is for a single designated person, and the kohen himself must perform it.
A single chatas cannot be used to effect kapparah for two people simultaneously. In addition, the kohen must perform the atoning acts himself; the service cannot be delegated in a way that removes the kohen’s personal agency from the kapparah.