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我理解是在中国填好表格寄回美国东部移民局，广州不受理对吗？

-Correct.

哪回寄如果填中国的地址吗？还是送邮件不需要邮寄？

我可以让在美国的家人帮我寄吗？回寄美国的地址？

-You do not need to have a reason to abandon your green card. You can file I-407 within US using your address in US. Then, leave US after you file I-407. You had better leave US before your I-407 is approved and thus, you do not have a unlawful presence problem. Your family can receive the correspondences from USCIS for you. 

See this link for I-407 filing in US (Read I-407 Instructions carefully and provide all the required documents for I-407 filing):

Record of Abandonment of Lawful Permanent Resident Status | USCIS

谢谢！