You can instantly add text to an existing note in Evernote or OneNote using the Zapier Chrome extension, allowing for seamless automation and saving time when working on projects or managing notes. The extension enables you to trigger automated workflows with a single mouse click, connecting your apps into customized workflows without requiring any coding knowledge. By installing the extension, logging into your Zapier account, and setting up a new Zap, you can easily add text to existing notes in Evernote or OneNote, making it an ideal tool for individuals looking to boost productivity and stay organized.