FfH: Age of Ice, how to create the weapon?

[Tuzak]

I have all 3 parts of the weapon within the starting city and I know where to find Mulcarn. However how do I mend the weapon?

 

[mindlar]

Take all 3 parts to a city with a forge. The parts may need to be on the same unit, though I'm not sure about that.

 

[SwordofStriker]

Once you have all three parts in a city with a forge, an icon should be available to create the God Slayer sword. All you do is click that and you get your hero unit with the sword.