I'd like to manually add some words or phrases to the keyboard's suggestions dictionary, and possibly remove some that have already been added. Is there a way to do this? Under the Keyboard settings app, I only see options to change the language and reset the suggestions dictionary entirely. Is there an app or other mechanism by which I can edit the suggestions at a more granular level?
Sometimes when you type a word that the phone doesn't know, if you swipe to the left of the suggestions, there is a '+'. Tap on that and it will add the word to the dictionary.
If the phone keeps auto-correcting your custom word, instead of pressing backspace and typing it again, tap on the corrected word, the first suggestion should be the custom word you typed. Doing this also sort of "trains" the phone to not auto-correct it again.
As others have mentioned the only way to remove custom words from the dictionary is to reset/remove all custom words.