Scripts for beginners.

If you need a hero from the map, use MakeHeroInteractWithObject.

Added 3 minutes later

And what does that mean? How do I put him there?

In the editor, press the English letter M. A window will appear. Go to PlayerProperties. Select the AI player to whom the Assassin hero belongs. At the bottom of the window, there will be an empty list called Reserve Heroes List. Click Add and create the Assassin hero there. An army is not required, as it is assigned in StartCombat.