Ask TWOCENTS:How to cancel H4 application?

After I filed the transfer from H1B to H4 application, I want to cancel my H4 application because my H1b is still effective. Now I received the receipt of H4 Application from USCIS. I am wondering what other materials I need to cancel my H4 application. If anyboday here can provide the sample letter to cancel H4 Application or give me some suggestion, I will be very appreciated.