Sorry we didn't get to your post sooner!
From the settings dialog you can open the hotkeys file. You can delete that file, or delete the contents so it's empty. Restart Spine and the hotkeys will be back to defaults. You'll find it under Files:
Loading Image
As you can see, in 4.0 there's a Defaults button which resets the hotkeys file, same as deleting the file. You'll still need to restart Spine if you click that though (we'll make that more obvious).
Before or after doing the above, if you are on macOS choosing QWERTZ for the keyboard type will change the hotkeys so you can use cmd+Z and not cmd+Y for undo.
