Follow these required steps to reset your First Bank USSD 5-digit PIN code,

1. Dial the code *894*0# on your registered mobile phone. Mtn, Glo, 9 mobile and Airtel.
2. Choose Reset your PIN (option 3)
3. Enter your ATM card PIN code
4. Then Change your 5-digit PIN to a new one
5. Receive a Successful message

This First Bank reset USSD code *894*0# works on all major mobile networks in Nigeria: Mtn, Glo, 9 mobile and Airtel in case your PIN is compromised.

You can read this post on Firstbank transfer USSD code and other useful codes