Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
If you don't remember the passcode/password, you can try changing the passcode from Amazon's Manage Content and Devices page.
You can change your Fire Tablet's lock screen password ***** PIN directly from Manage Your Content and Devices. Follow the steps below;
If that didn't work then have to reset your Kindle to factory settings. Unfortunately that is your only way to access your Kindle.
Resetting will erase everything from it, but you can re-register it with the same Amazon account you used on it to redownload your books without paying again.
Enter the incorrect password ***** for 6 times and it will ask you to reset it. If not, enter any of the passwords below to reset;
After resetting the kindle, you can redownload all your books to it using the same account you used to purchase them.
Please let me know if that didn't work, so we can continue troubleshooting.