可以发信给移民局（邮寄到你目前 I-485 申请所在的地方，一般是 USCIS Service Center 或者 National Benefit Center），参考下面的内容：
Dear USCIS Officer,
I’m writing to transfer the underlying basis of my currently pending employment-based I-485 adjustment of status application to my approved（注：如果 EB2 I-140 还没有批准，在这里写 Pending 而不是 Approved) I-140 petition in EB-2 category, from the previous basis of I-140 in EB-3 category, following USCIS instructions in Policy Manual, Volume 7, Part A, Chapter 8 (https://www.uscis.gov/policy-manual/volume-7-part-a-chapter-8 )
My name is ABC XYZ. My I-485 case# is______ , my A# is _______. Please see the documents enclosed:
(1) Copy of my I-485 receipt (2) Copy of my I-140 approval notice (or I-140 receipt) for immigration petition in EB-2 category, for which I am the beneficiary.
Please contact me at ____ if you have questions. Thank you for your attention.