This article explains the different lock screen options on the Amazon Fire tablet and how to set them up. It also covers how to unlock your device if you forget your code.
Amazon Fire HD 8/10 Tablet: FORGOT YOUR PASSWORD? HOW TO RESTORE FACTORY SETTINGS TO ORIGINAL DEFAULT SETTINGS
With a password on your lock screen, turn on the device and enter the password to gain access. With a PIN, turn on the device and enter the PIN to gain access.
If you've forgotten your Fire tablet password or PIN, you can still regain access to your device by following these steps.
While on the lock screen, enter an incorrect password or PIN five times.