Green Card after Renewal

[HB_Resident]

I renewed my GC last summer in the US, and recently returned to LAX with a renewed GC. A USCBP officer told me to returne my expired GC to an office of USCIS after I had answered for his question where my old one was.

(Q) Where shall I mail my expired GC (with a sticker for temporary extension)? Is there any form or instruction on the USCIS web?

The officer did not tell specifically where I have to mail it. Is it just District or its sub-office? Or, the LA Lockbox? I don't think there was an instruction when I received a new GC.

BTW: I was sent to the second inspection booth as a machine of the officer could not read my new GC properly.