To access the user dictionary on a Kindle Fire, go to the keyboard settings on the device. First, tap on a text box, such as the search text box at the top of the home screen, to activate the on-screen keyboard.
Tap and hold down the space button on the on-screen keyboard to get the Select Keyboard Language screen, then tap the Keyboard Settings button at the bottom of the screen to get the list of different keyboard settings. "Personal Dictionary" is the last entry on the list. Tap on it to gain access to view, edit and delete words in the user dictionary.