An epic simile will take place over several lines. It contains the same measure of a simile in that there must be a comparison that begins it, often using like or as. In Book 1, here is a simile about Athena:
So saying she bound on her glittering golden sandals, imperishable, with which she can fly like the wind over land or sea; she grasped the redoubtable bronze-shod spear, so stout and sturdy and strong, wherewith she quells the ranks of heroes who have displeased her, and down she darted from the topmost summits of Olympus, whereon forthwith she was in Ithaca, at the gateway of Odysseus' house.
Over several lines the simile grows its power. It began simply by comparing Athena's speed to the wind. This is further developed by the words darted and later whereon forthwith. Each of these words suggest the speed that the original simile cited.
In Book 2, the first paragraph contains an epic simile:
NOW WHEN THE child of morning, rosy-fingered Dawn, appeared Telemachus rose and dressed himself. He bound his sandals on to his comely feet, girded his sword about his shoulder, and left his room looking like an immortal god. He at once sent the criers round to call the people in assembly, so they called them and the people gathered thereon; then, when they were got together, he went to the place of assembly spear in hand—not alone, for his two hounds went with him. Athena endowed him with a presence of such divine comeliness that all marveled at him as he went by, and when he took his place in his father's seat even the oldest councillors made way for him.
In this simile, Telemachus is compared to a god. His appearance in dressing developed this. It is further developed by the words presence of such divine comeliness and all marveled at him and even the oldest councillors made way for him.
The only simile I find in Book 3 is a stretch for an epic simile because it does not develop as much as the others, but it performs the function of comparing Telemachus once again to a god:
Meanwhile lovely Polycaste, Nestor's youngest daughter, washed Telemachus. When she had washed him and anointed him with oil, she brought him a fair mantle and shirt, and he looked like a god as he came from the bath and took his seat by the side of Nestor. When the outer meats were done they drew them off the spits and sat down to dinner where they were waited upon by some worthy henchmen, who kept pouring them out their wine in cups of gold. As soon as they had had enough to eat and drink Nestor said, “Sons, put Telemachus' horses to the chariot that he may start at once.”