Book-In Labels can be reprinted by accessing either the Ready to Read or Incubator Contents list (note that if the labels you want to reprint are for plates that are not ready to be read, you will have to use the Incubator Contents list), and right-clicking on the Book-In you wish to reprint labels for:

Then select 'Re-Print Book-In Labels' from the right-click menu.

If a printer has been set in the configuration, the Labels will now be printed using this printer, otherwise you will be prompted to select one from the list of installed printers.