Do you mean he doesn't know the spell, or he doesn't have summoning magic, or there's no free skill slot?

Are you stuck again?

Describe the hero and how many units you can gather in the army, and I'll think about how to complete it. There's always a solution.

No, I don't kill everyone along the way because you can lose a lot of units, especially the ones you need. Or, if I know who they are, I can easily defeat them without losses. Try lowering the difficulty level for this mission. I only return when I'm nearby, for example, on a ship. You can return to the island with units in 3 days, but you have to do it towards the end of the week so you don't have to run back and forth many times.