USCIS recently noted to the public that it erroneously scheduled certain customers for more than one Application Support Center (ASC) biometric appointment. USCIS guides applicants who have already attended an ASC biometric appointment and received a second appointment notice to contact the National Customer Service Center at 1-800-375-5283. USCIS will be able to inform you if you are required to return to have your biometric data collected again.
If you have not yet attended your ASC appointment and received more than one ACS appointment notice, you should attend just one of the appointments, but bring both notices with you to that appointment.