When you press and hold on a cell to enter notes, or when you click on "Enter a new note" in the Tech Notes section, the keyboard will pop up. You will see a microphone icon to the left of the spacebar which.
When pressed for the first time, will open the window to allow the access to the voice recognition. Next time, the voice recognition will start automatically.
Now as you speak the text will appear in the text field. At the end tap microphone icon in the middle of the screen to stop voice recognition. Check the text and, if needed, change it. Then tap 'Next' / 'Done' to save information and move to another field.