You came to the right place! I'm not sure if you're referring to the lock screen password or Parental Controls, so I'll provide steps for both.
To reset your lock screen password, if you enter the same wrong password or PIN five consecutive times, you should be given the option to reset your lock screen PIN. You will need to enter your Amazon account password in order to reset their lock screen password.
You can also reset your PIN from Manage Your Content and Devices.