How does the free attack from Lead the Charge work?

Question

Accepted Answer

After you attack, a nearby hero gets a free attack that costs none of their actions. It happens after the first attack and any counterattack have fully resolved, not at the same time, and the second hero may pick any target they can reach, not necessarily the same enemy.

The Lord of the Rings: Journeys in Middle-earth

How does the free attack from Lead the Charge work?