I know banks are not on our necks right now to link BVN & NIN but you might need to know your BVN sha.

The general code to check BVN is *565*0#.

Network Requirement Action
MTN: Phone number used in registering for BVN and account balance of 20 Naira, Dial *565*0# and enter your date of birth
Airtel: Phone number used in registering for BVN and account balance of 20 Naira, Dial *565*0#
Glo: Phone number used in registering for BVN and account balance of 20 Naira, Dial *565*0#
9Mobile: Phone number used in registering for BVN and account balance of 20 Naira, Dial *565*0#

Source: https://www.loanspot.ng/how-to-check-bvn/