During these seven days the cohein gadol sprinkles the karbanos, burns the ketores, prepares the lamps and brings the head and back legs of the karban tamid. The whole year the cohein gadol may optionally do these avodos.

Yuma 1:3

Several elders from the bais din would read before him the avoda of Yom Kippur [the work of the karbanos]. They would tell him to read the parsha as maybe he forgot some details.

The morning before Yom Kippur they put him by the eastern gate and brought him the different animals so he should know which animal to use for what.