What do you mean by "iTunes device" - I'm guessing an iPad or iTouch or iPhone, but which? What operating system is on your device, and on your computer? What ebooks do you have, what format are they in, where did you get them from, where are they now (in Calibre, I'm guessing?), and what do you want to do with them now - I'm guessing get them onto your device? What app do you want to read your books in on your device?
Have you read this thread?
https://www.mobileread.com/forums/sho...d.php?t=118559
and this one?
https://www.mobileread.com/forums/sho...d.php?t=225552