TT points to the first offering of the miluim — the chatas bull — with semichah by Aharon and his sons and the blood application by Moshe.
ויגש את פר החטאת ויסמך אהרן ובניו את ידיהם על ראש פר החטאת — סמיכת אהרן ובניו. וישחט ויקח משה את הדם ויתן על קרנות המזבח סביב באצבעו — משה עובד בדם החטאת של המילואים.
“And he brought near the bull of the sin-offering, and Aharon and his sons laid their hands upon the head of the bull of the sin-offering. And he slaughtered it, and Moshe took the blood and put it upon the horns of the altar round about with his finger…” — Aharon and his sons perform semichah; Moshe performs the blood service of the miluim chatas.
Custom — narrative of the first miluim offering.
The chatas bull of the miluim receives semichah from Aharon and his sons; Moshe alone performs the blood service on the altar.