Currently Being ModeratedOct 8, 2011 2:52 PM (in response to sg_)
depending on what you're trying to do, you can go into you settings and erase all the words and it sets it to the default words. (this would be if a word keeps popping up that you don't want that you might have typed one time and accepted and now auto correct thinks it's a word that you want to type)
or you can try tricking the iphone by writing those words in safari and searching for it it. This will be saved probably until you clear your cache. Here's a link to the trick: http://www.theiphoneguru.net/2010/08/06/how-to-easily-add-words-to-the-iphones-a utocorrect-dictionary/
if you know there is a word you always want, I've heard of people adding in a fake contact in the contacts list, which the iphone will always remember like all of the names in your contacts.
At this current time there is no explicit way iOS can natively have it's autocorrect library editted.
Currently Being ModeratedOct 8, 2011 4:06 PM (in response to sg_)
It will eventually learn the words you use. Just tap the x from the autocorrected word and use the one you typed in. It will stop autocorreccting that at some point. Doesn't take too long, 3-5 times.
Currently Being ModeratedFeb 20, 2012 9:25 AM (in response to sg_)
iOS learns new words much faster than it unlearns them, unfortunately. But I have just stumbled on a way to help an iPhone (or other iPad, iPod touch, etc.) unlearn a word it has mistakenly learned. This requires iOS 5.0 or higher.
Suppose your young daughter thought it would be fun to type "yöü" instead of "you". Sure enough, after a few times the phone learns that when you type "you", or "yoi", "yu", "tou", "tiu", etc., you really mean "yöü". (Grr.) The cleanest way to unlearn this is to go to Settings > General > Reset > Reset Keyboard Dictionary. The problem with this, of course, is that it resets everything that it has learned about your typing, which you may not want to do.
Here is the workaround to unlearn a specific wrong word:
1) Go to Settings > General > Keyboard > Add New Shortcut...
2) In the phrase field, enter the correct word (e.g., "you")
3) In the Shortcut field, enter the keystrokes that tend to bring up the incorrect word (e.g., "yoi").
4) Tap Save.
5) Repeat steps 2-3 for each set of keystrokes that tends to product the unwanted word (e.g., "yu", "tou", "tiu", etc.).
6) Open a new note in the Notes app and test. You'll see the proper word now gets suggested instead of the incorrect one.
Interestingly, if you then go back to Settings > General > Keyboard and delete the shortcuts you added above (by stroking them out with your finger and tapping Delete), and then repeat step 6, you'll see that the phone appears to have largely unlearned its bad habit. It seems that adding the shortcuts helps override the learned behavior, even after the shortcut is deleted. But you certainly don't need to delete the added shortcuts if they are not bothering you.
For good measure you can also add a shortcut with the correct word ("you") in the phrase field and the incorrect one (e.g., "yöü" in the shortcut field). I'm not sure if this helped, but based on my theory above it might help too. All I know is I did all of the above and now the incorrect word rarely (but not quite never) gets proposed when typing. Yay!