how to get the Tax Registration Numbers in the Purchase order Report.

I am Trying to get the Tax Related Details in  to the Purchase order Report.

I am Creating One New Method in the PurchPurchaseOrderHeader Table called 

private void initfromTaxInformation_IN(TaxInformation_IN _taxInformation_IN,TaxRegistrationNumbers_IN _taxRegistrationNumbers_IN)
{
//TaxRegistrationNumbers_IN taxRegistrationNumbers_IN = TaxRegistrationNumbers_IN::find();

//this.TIN = _taxRegistrationNumbers_IN.RegistrationNumber;
}

but i  am getting the Errors.

How to get the Correct data.