Every time you reject a word that your iPhone’s Auto-Correction feature suggests by closing the Auto-Correction bubble, the word you’ve chosen instead is added to the feature’s memory. Resetting the device’s keyboard dictionary returns the dictionary to its default state, which automatically erases the Auto-Correction feature’s memory. You are then free to repopulate the dictionary with the correct words. In addition, use the Shortcuts feature — an iOS 8 assistive technology — to directly add words to the dictionary.
Reset the Auto-Correction Feature
Open your iPhone's Settings screen and select General from the list of settings.
Tap Reset, which is the last item at the bottom of the screen, to open the Reset screen.
Select Reset Keyboard Dictionary from the options. If your iPhone is password protected, the Enter Password screen opens.
Enter your password if prompted to do so.
Select Reset Dictionary in the pop-up box to confirm the keyboard dictionary reset.
If you prefer not to use the Auto-Correction feature, disable it through the Keyboards screen. Open the Settings screen, select General and then tap Keyboard to open the Keyboards screen. Slide the Auto-Correction switch to the Off position.
You can also disable the Predictive Text feature from the Keyboards screen. Browse to the Keyboards screen and then slide the Predictive switch to Off.
After you add a word to the list of shortcuts, typing the word's first letters prompts the Auto-Correction feature to suggest the word.
Open the Settings menu and select General.
Scroll down the screen and select the Keyboard option.
Tap Shortcuts to open the Shortcuts screen.
Tap the Plus icon to proceed to the next screen to create a new shortcut.
Enter the word that you want to add to the keyboard dictionary in the Phrase field. Leave the Shortcut field empty and then tap Save to save the word and return to the list of shortcuts. Tap the Plus icon again to add another word.
Resetting your keyboard dictionary also erases your list of shortcuts.