How to import existing system tool into my new python tool?

I want to import existing "Feature to 3d by attribute" tool into my new python tool which I am creating. I know it is 100% possible, but I can't find a way how to do it.

Anyone could help me with this situation?

$ import arcpy import sys

class Toolbox(object): def init(self): self.label = "Konvertuotojas" self.alias = ""

    # List of tool classes associated with this toolbox
    self.tools = [Konvertuoti] 

class Konvertuoti(object): def init(self): self.label = "Konvertuoti taskus" self.description = "Konvertuoja taskus du i tris dimencijas"

def getParameterInfo(self):
    #Define parameter definitions

    # Pirmas parametras ivesties
    in_features = arcpy.Parameter(
        displayName="Input Features",
        name="in_features",
        datatype="Feature Layer",
        parameterType="Required",
        direction="Input")

    in_features.filter.list = ["Point", "Polyline", "Polygon"]

    # Antras parametras stulpelio ivestis
    field = arcpy.Parameter(
        displayName="Field name",
        name="field_name",
        datatype="Field",
        parameterType="Required",
        direction="Input")

    field.parameterDependencies = [in_features.name]
field.filter.list = ["Short", "Long", "Double", "Float", "Text"]

    # Trecias parametras isvesties
    out_features = arcpy.Parameter(
        displayName="Output Features",
        name="out_features",
        datatype="Feature Class",
        parameterType="Derived",
        direction="Output")

    out_features.parameterDependencies = [in_features.name]
    out_features.schema.clone = True

    parameters = [in_features, field, out_features]

    return parameters

def isLicensed(self): #optional
    return True

def updateParameters(self, parameters): #optional
    if parameters[0].altered:
        parameters[1].value = arcpy.ValidateFieldName(parameters[1].value,
                                                      parameters[0].value)
    return

def updateMessages(self, parameters): #optional
    return


def execute(self, parameters, messages):

CODE HERE

arcpy.FeatureTo3DByAttribute_3d(in_features, out_features, field)?????????????
    return

$