John Gill Commentary Leviticus 9:15

"And he presented the people`s oblation, and took the goat of the sin-offering which was for the people, and slew it, and offered it for sin, as the first." — Leviticus 9:15 (ASV)

And he brought the people's offering
To the altar, having offered his own first: and took the goat, which [was] the sin [offering] for the people,
and slew it ;
where he had slain his own: and offered it for sin, as the first :
the first offering he offered for himself, which was of the same sort.