This feature is only available if it was properly activated in the Services Preferences
dialog.
Please follow these instructions to activate the context menu.
Once activated, proceed as follows:
Control
key on your keyboard and click inside one of the selected file icons (if your mouse has a right mouse button, you can right-click instead).A Better Finder Rename 12...
The application will now launch automatically and the preview table will already contain all the selected files. the bottom of the preview list to bring up a file selection dialog.