TouchID is not a substitute for a Passcode.
TouchID/FaceID require a Passcode to be set prior to configuring the biometric authentication. The device Passcode serves two purposes; it is used to create an encryption key that protects your biometric data - and provides a fallback authentication method if biometric authentication methods cannot be used.
The Passcode is used to enable the Secure Enclave (security chip) of the device. The passcode, unlocks the Secure Enclave - and releases the encryption keys that secure your encrypted biometric authentication data. After a system restart, your Passcode will always be required.
If your Passcode has been forgotten you’ll have no alternative other than than to follow this process:
If you’ve forgotten the passcode on your iPad, or your iPad is disabled – Apple Support
You’ll need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS).
You may also need your AppleID and associated password. If these have also been forgotten, they can be recovered here:
https://iforgot.apple.com
To recover your credentials, you’ll need access to one of the following:
- Your primary email address mailbox that corresponds with your AppleID
- Any of the secondary/recovery email addresses that should be configured for your AppleID account
- Any of the trusted telephone numbers (fixed line or Cellular/Mobile) that are associated with your AppleID
Unless you AppleID account has not been fully/correctly configured, or has been seriously neglected, recovery of the AppleID and password should not be difficult.
More information about recovery of your AppleID:
If you forgot your Apple ID - Apple Support
More information about recovery of your AppleID password:
If you forgot your Apple ID password - Apple Support
When you recover access to your credentials, you would be well advised to log-in to your AppleID account from a web browser - and verify/update any email addresses and trusted telephone numbers:
https://appleid.apple.com