Effective February 1, 2019, we no longer accept local filings of Form I-407 Record of Abandonment of Lawful Permanent Resident Status from U.S. green card holders who wish to relinquish their status. If you wish to file this form, you may do so by mail or directly with a U.S. Citizenship and Immigration Services (USCIS) office. For Singapore, the closest USCIS office is in Bangkok, Thailand. You may find more information about that office at https://www.uscis.gov/about-us/find-uscis-office/international-offices/thailand-uscis-bangkok-field-office.
To complete the process with USCIS, you will need to complete the Form I-407, “Abandonment of Lawful Permanent Resident Status”. Instructions can be found at Form I-407 Instructions.