You can delete Labor Items from your SI 2017 Catalog individually or you can delete multiple Labor Items at one time using the Delete button. You can select multiple Labor Items in the grid use by holding down Shift (to select a series) or Ctrl (to select outside of a series).
You can also right-click to delete, or use the keyboard shortcut Ctrl+Del.
There is no "undo" in SI 2017. Once deleted, there is no recovering these Labor Items unless you restore a backup of your SI 2017 server.