While editing, you can make mistakes that you don't realize right away. One of these is cropping off part of a word that you didn't mean to.
If you don't notice right away, you could be convinced that you needed to undo all of your edits up to that point but that's not the case! When you ripple delete in ScreenFlow, it saves the portion of the clip that you deleted. All you have to do to recover that clip is to select the clip and drag it. Then you can make your desired edits again