The elders of the congregation, i.e. the rulers of the people, of whom see Exodus 3:16, Exodus 24:1, who here acted in the name of all the people, who could not possibly perform this act in their own persons.
Related Commentaries of Leviticus 4:15
Leviticus 4:15
15 And the elders of the congregation shall lay their hands upon the head of the bullock before the LORD: and the bullock shall be killed before the LORD.