Android Studio undo (Ctrl-Z) / redo (Ctrl-Y) not working

With the help of this answer, I have worked it out…

1. Go into Settings (Ctrl+Alt + S)
2. Type Redo in the search box.
3. Double-click on the Redo result
4. Select Add Keyboard Shortcut
5. Press Ctrl+Y
6. Click OK
7. Click OK