H1 to H4 COS Pending, Want to withdrawn the COS since got a project with same employ

[Iamforgc]

I was on H1 until jun1. Applied change of status to h4 on june2nd, still it is pending....my previous employer not cancelled h1 which is valid until dec 2015. Now he got a project for me which is going be to start from monday. So can I start work with him on earlier h1b. and request for H1 to H4 COS withdrawal? can you please let me know the process for COS with drawal. also please give me some sample document if you have any?

Thanks in Advance