Gst challan

Sir, I wanted to know how to create a challan as a subcontractor . To ellaborate i have an agreement with a company to provide a service, however due to some constraints we outsourced the said service to a subcontractor. So the subcontractor bills us and we inturn bill the company. Now the subcontrator charges us GST by raising a invoice and we inturn charge the company GST by raising a separate invoice. Now how do we pay the GST ( The mechanism) Hope that i get help in understanding and raising a challan to pay GST