select all notes in the region in the Piano Roll area by pressing CMD-A. mute all of these notes by pressing CTRL-M. deselect all notes and then select the ones you want to hear.
How do I select notes in Logic Pro X?
You must select note events before you can edit them. You can select notes by clicking, Shift-clicking, dragging to make a marquee selection, and using the keyboard at the left edge of the Piano Roll Editor.