Well, your Call Function node uses a string parameter, but none of your functions (at least those you showed) fits the defind parameters.
If your equipped class is stored in the schematics Local selected data, you'll not be able to access it in your script. E.g. use Global selected data instead and you can access it via Maki.Game.SelectedData.
Or, to make it a lot easier, if your script is attached to the combatant, you can simply get the combatant from the game object like this:
Combatant combatant = ORKComponentHelper.GetCombatant(gameObject);
And afterwards make all the changes on it however you like. Learn more about combatant scripting in this documentation.