The PIN number is the 4-8 digit password you registered when you first set up your Biometric Wallet.
Please note that if the authentication attempts fail multiple times (5 fingerprint attempts + 10 PIN attempts) on the Biometric Wallet, the wallet will be automatically initialized for security purposes and all keys in the wallet will be deleted.
In this case, you can use the mnemonic code (24 recovery words) you have stored to recover the wallet and regain access to your assets.