What does the prophet Teiresias tell Odysseus to do when he finds the herds of Helios?

After spending about a year with her, the goddess Circe tells Odysseus to seek out the blind prophet, Teiresias, in the Underworld in order to procure instructions for how to make it safely home to Ithaca.  Odysseus carefully follows her directions, sacrificing animals and allowing their blood to draw the spirits toward him, allowing none of them to approach the blood until he could speak with the prophet.  When he does, Teiresias tells him that, when Odysseus arrives at Thrinacia and finds the sacred herds of Helios, he must "leave these unharmed and heed [his] homeward way."  If they follow this advice, there is yet a chance that they will make it back to Ithaca, though the way will be very hard (because Poseidon is holding a grudge due to the fact that Odysseus and his men blinded Poseidon's son, Polyphemus, the Cyclops).  If, however, either Odysseus or his men fail to take this warning to heart and harm even one member of the herd, all of the crew will perish.  Circe repeats this warning when Odysseus returns to her home after he leaves the Underworld.