Calibre has a tool built in if you do not want to use the command line (assumes the 2 devices can see each other on a LOCAL network and can move/copy files between these 2 systems).
DO NOT USE
ADD if you have a working Library copy available.

You lose your previous Metadata edits
https://manual.calibre-ebook.com/faq...ter-to-another
Caution: Do not do this TO A (target) Library with books that don't exist in the source Library. It replaces everything.