How do I remove heroes from the creature banks?

That's actually the fun part: you attack with a scout, and there's a standard pack there, then you attack with your main army, and there might not be 120 gargoyles with 850 hit points. But after the victory, in addition to the standard resources, your army also joins you (gargoyles join the gargoyles, harpooners join the dwarves, etc.), but most often these battles don't pay off).

 

Oh, and the buttons at the start of the map (guards) are not active, meaning you can't uncheck the box.