Work Contract

Andrio Kyong (24 Points)

29 May 2020  
In work contract while awarding the order by Govt Dept (Govt Dept registered as TDS Deductor)and submitting the invoice by the contractor the tax rate was considered 18%.
Now the Government Dept is releasing the payment on completion of the work as per the invoice with GST18% but now we found out that tax rate should be only 12%. What can or should be done here to retify the error?