No mattter how many times you go back and type the word? In that case, once you finish typing the word and ensure you have it spelled correctly, and BEFORE you hit the space or punctuation keys, tap the word as you typed it in the predictions selections above the keyboard. That adds it to your personal dictionary and will recognize it then and in the future.
The flip side of this is that you can long press any word in the predicitions to no longer have it suggested (for excample if you saved a typo or misspelled someone's name previously).
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