So click 'Edit Part', then those 3 Dots next to 'Preview' 

- & try the options I haven't described yet, if interested 

( I can't describe more of them because I haven't tried 'Cast' or 'External link' option - but I'm just telling you that 'they are possible' - & you may try them yourself & use them - if you find any of them useful for Your Book :) )