The conversion preview shows directly above your text to offer live recognition feedback and word suggestions.
Use it to edit a word or character that isn't right: Tap it and it will open a list of suggestions. From the list, select the word or character you were looking for.
If you are using a word that is particularly specialized it may not appear in the suggestion list. If this is the case you can enter the word into your text by using the keyboard or, if you intend to use the word regularly, you can enter it into the user dictionary (not available with Nebo free version on iOS).
You can activate/deactivate the conversion preview anytime you want in the Settings section of the side panel.