When Odysseus sees him in the Land of the Dead, Achilles doesn't really have a message for him, but wonders why Odysseus has ventured to such a horrible place. Odysseus tells him he's there for information from Tieresias, but praises Achilles and tells him not be be disheartened because he's dead. He is still the prince of the underworld. To that, Achilles answers, "I would rather be a paid servant in a poor man's house and be above ground than king of kings among the dead." In other words, he'd do anything to be able to live again, rather than have it all in the land of the dead.
The only other thing he wants to know from Odysseus is how both his father and his son are doing. Odysseus gives him good news about his son's valiant efforts at war. And then Achilles leaves him.