You just write a letter to USCIS service center where your I-485 is pending. It is not cancellation of I-485; you need to withdraw the pending I-485. Write your name, Pending I-485 receipt#, your DOB, your A number that is on I-485 filing receipt notice on top of letter and make a request that you want to withdraw the pending I-485 and attach the copy of I-485 filing receipt. Write the date and sign the letter. Send the letter to USCIS where your I-485 is pending. Make copy of the letter after you sign the letter and keep the copy of the letter for your records.
I feel as if I am struck by a lightning. First I lost my opportunity to get my labor cleared during July 2007 fiasco (my file was closed). Then this harsh reality which I am not able to digest. My EB3 PD June 2002 India. I calculated and found that total pending GCs before my date are 3815. How many GC are allocated to EB3 category to India per year. If from the numbers I feel it may take years then I will just return back to India.