Apple Logic Pro X - Manual (Page 667)

Chapter 20 View and edit music notation 667
Add and edit fingering dots
You can add, edit, and delete fingering dots on a chord grid.
Add a fingering dot
m Click the string and fret.
A black dot is created.
Move an existing fingering dot
Do one of the following:
m Click another fret on the same string.
m Drag the dot to a new fret position.