Apple Logic Express 9 - Manual (Page 919)

To define the finger number on a fingering dot
µ
Control-click (or right-click) a dot, then choose a number between 0 and 5.
To create an optional fingering dot
Do one of the following:
µ
Option-click a string to create an optional dot. If another real dot exists on the same
string, the real dot remains.
919 Chapter 31 Working with Notation