Kindle Fire HD 8.9 not getting unbricked after going into fastboot mode
From my understanding, if you can't boot into recovery by first pressing the volume down button and holding it, while pressing and holding the power button, your tablet is lost. You will need recovery to flash the firmware that came with your tablet, if I am not mistaken. If there is another way, you might want to wait for another answer. If your tablet is still under warranty, send it back to Amazon for a one time courtesy replacement.