Note that find and replace work on entire shapes at the same time. But keep in mind that a shape could have multiple text labels and each individual text label could match the string to find or the string to replace multiple times (at least when you look for a substring). When you want to find or replace within a single text label or table cell, you should load that text label first in the out-line text editor and then do a find or replace within that dialog.
Note also that you can fill an empty string for the string to find in both dialogs. An empty string matches only the text shapes that are empty. You can also fill in an empty string in the replace with text field, providing that the string to find field is not empty.