You can set Keynote to automatically replace certain text with text that you specify. For example, you can have Keynote replace teh with the or (c) with © as you type.
You can also replace all instances of specific text in your presentation with other text you define.
Choose Keynote > Settings (from the Keynote menu at the top of your screen).
Click Auto-Correction at the top of the settings window.
In the Replacement section, select the tickbox next to “Symbol and text substitution”.
Click 
, then type the text you want to replace (such as “teh”) in the Replace column.
In the With column, type the word you want to replace it with (such as “the”).
You can also use emoji and symbols as replacements.
Press Return to save the change.
These text substitutions apply only to Keynote.
If you want to replace specific text that appears in multiple places in your presentation, you can add the replacement text to your computer’s Keyboard settings, then use the Substitutions window to replace the text wherever it occurs.
With the presentation open, choose Edit > Substitutions > Show Substitutions (from the Edit menu at the top of your screen).
In the Substitutions window, select the Text Replacement tickbox, then click Text Settings.
macOS Ventura 13 or later: In the Keyboard setting, go to Text Input, then click Text Replacements.
macOS 12 or earlier: In Keyboard preferences, click Text.
Click , then type the text you want to replace (such as change) in the Replace field.
Type the word you want to replace it with (such as modify) in the With field.
After your last entry, click Done, then close the settings window.
Do one of the following:
Replace all occurrences of the text: In the Substitutions window, click Replace All. If you have other substitutions in Keyboard settings, they are also applied to your presentation.
Apply replacements to specific text: Select the text you want to modify, then in the Substitutions window click Replace in Selection.
Note: Text replacement settings in Keyboard settings apply to other applications on your computer, such as TextEdit, Pages and Numbers, when they have text substitution turned on.