An ICTPlayer is ContentTweaker's special IPlayer object.
That means all of IPlayer's methods are also available on this object!

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import mods.contenttweaker.Player;

IMutableItemStack getHeldItem(Hand hand);

Parameters:

• Hand hand → Main or Off Hand

Returns the IMutableItemStack held at the given Hand.