Dictate correspondence in Office apps

1. Sign in to your Microsoft account using a mic-enabled device and a supported browser (Edge, Firefox, or Chrome).
2. Go to Home > Dictate (the button that looks like a microphone) in the app you want to use (Word, Outlook, PowerPoint, etc.).
3. Wait for the button to turn on and start listening.
4. Move your cursor to where you want to insert text and start speaking to see text appear on the screen.

Click here for more information from the Microsoft support site