Whenever a cohein entered the azara for the avoda, he had to go to the mikvah.

On Yom Kippur, the cohein gadol went 5 times to the mikvah and 10 times to wash his hands and feet. All was in the holy in bais haparva except for this one.

Yuma 3:4

They spread out a linen sheet between him and the people. He went to the mikvah got up and dried himself. They brought him his golden clothes which he then put on and was mekadesh his hands and feet. They brought him the korban tamid. He started the slaughtering of the animal and another cohein finished the slaughtering. The cohein gadol received the blood and sprinkled the blood.

He went to burn the ketores and clean the menora. Then he offered the animal, chavitim and the wine.