Was it the SIM card PIN or the phone's security code?
If it's the SIM PIN, the default PIN is 3436. If you changed it, then, you can enter the wrong SIM PIN 3 times and the phone will then ask you for the PUK code which can be acquired via customer service either via phone, chat or e-mail.
If it's the phone's security code, the default code is 00000000 (0 eight times). If that doesn't work, you would have to send your phone in for repair for Samsung to reset it for you.