We've made some wording changes to this feature to avoid confusion and make it easier to explain. We're no longer calling this process "exporting" and "importing", since that's something you may have to do to the file itself. The button in the Document Preferences window is now "Switch to a Different Word Processor…".
https://www.zotero.org/blog/move-zotero-citations-between-google-docs-word-and-libreoffice/