In Microsoft Word, the Zotero plug-in creates an additional tab or toolbar. The plugin is bundled with Zotero and should be added automatically when you install Zotero. If it does not here are the most common resolutions.
If the Zotero menu is not visible in your Google Document, try one of these options.
Zotero provides a thorough help page for the LibreOffice suite.
Please note Zotero requires LibreOffice 5.2 or later. Apache OpenOffice and NeoOffice are not supported by Zotero.
There are several reasons you might be getting an error message when deleting or modifying your document. Consult this list of troubleshooting errors to determine a potential fix.
If you are not able to find an answer to your issue here, the Zotero community has a robust knowledge base and discussion forums. Most answers to issues can be found in there.