I added password_table as an attribute to the CreatePassword class.

class CreatePassword(ttk.Frame):
    def __init__(self, parent, password_table):
        super().__init__(parent)

And satisfied it in the App() component.

# App class inherits tkinter
class App(tk.Tk):
    def __init__(self):
        super().__init__()
        self.title('Password Manager')
        # Add Components
        self.header = Header(self)
        self.savedpasswords = SavedPasswords(self)
        self.createpassword = CreatePassword(self, self.savedpasswords.password_table)

This seems to work and I am able to add the values to the table.