Leviticus 16:33-34

World English Bible

³³ Then he shall make atonement for the Holy Sanctuary; and he shall make atonement for the Tent of Meeting and for the altar; and he shall make atonement for the priests and for all the people of the assembly.

³⁴ “This shall be an everlasting statute for you, to make atonement for the children of Israel once in the year because of all their sins.”

It was done as Yahweh commanded Moses.