If this is a new local database, you can just sync.

If there's existing local data you're trying to overwrite, you'd want to first close Zotero and delete 'zotero.sqlite' and 'storage' in the Zotero data directory, and then sync.

Awesome!

This worked beautifully for me.
I reinstalled my OS and was not able to get Zotero to recognise the old files when I pasted them back into the directory after reinstalling it.

This method put everything back into place by syncing with the online server and even restored all of my notes and PDF files attached to the references! :'D