To remove typos accidentally added to a computer's dictionary on Windows and macOS, users can access their personal dictionary settings in the operating system's settings or preferences menu, where they can clear or delete individual words from the custom dictionary. For Microsoft Office apps, users must click on Options or Preferences, navigate to Proofing or Spelling & Grammar, and then select the Custom Dictionaries option to find and remove unwanted words. Google Workspace apps also have a similar process for removing custom dictionary words by accessing the Personal dictionary settings in the Tools menu.