Immediately after you scan, your reading is shown on the screen.
Top right is a small blue square with the pic of a pencil inside it.
Tap that pic, and the Add Notes screen comes up.
Never used it myself, but presumably it will be fairly intuitive.
I hope.
Edited to add. Oooh. Had a rummage. VERY useful. will be using it myself from now on. notes for food, fasting, reminders to check bg in 1 or 2 hours... veeeerrrrryyyy interestink
Linda, the code to get into the professional settings is CAA1C. No idea why they don't make that common knowledge as I'm always jiggling ratios around and having to update them on the Libre.