I have the dark knight dragon and I have a dark sword. It says I can use the dark sword to empower the dark knight but I can’t figure out how to do it. Suggestions appreciated

Holy knight also has that, but I was told it's just part of the description.

The dark sword is nothing but a decoration. You needed the Dark Knight to do the quest to get orbs as well as the rescue. Those orbs are what you needed to be able to empower him.

@nynaevelan thanks that’s what I needed to know