You can dictate text in Keynote when dictation is turned on in Dictation & Speech preferences on your Mac.
To learn how to set up and use dictation, see Mac Help. Click the desktop to switch to the Finder, choose Help > Mac Help (from the Help menu at the top of your screen), then search for “dictation.”
Choose Edit > Start Dictation (from the Edit menu at the top of your screen), then follow the setup instructions to configure dictation on your Mac.
Note: You can’t dictate directly over placeholder text. First, delete placeholder text (select it, then press Delete on your keyboard), then place the insertion point where you want to begin dictating.