Which operating system are you working with, and what specific versions of Word and Zotero?

Start here:
https://www.zotero.org/support/word_processor_plugin_troubleshooting#zotero_toolbar_doesn_t_appear

No, I mean the specific version numbers, like Zotero 5.0.53 and Word 2007 12.0.6787.5000.

Word 2007 is not supported, I'm afraid: https://www.zotero.org/support/system_requirements#word_processor_plugins

Right, but Microsoft no longer supports Word 2007, and there are issues with Word 2007 that sometimes prevent Zotero from working with it, but which Zotero can’t really do anything about (hence why Word 2007 is not supported). I recommend you update to a current version of Word (2010 or higher).

Tôi đang sử dụng Word 2019 và zotero 5.0 nhưng k kết nối được giữa word và zotero, nhờ bạn giúp đỡ!

Start here https://www.zotero.org/support/word_processor_plugin_troubleshooting#zotero_toolbar_doesn_t_appear

Zotero definitely works with Word 2016. Start here for troubleshooting steps https://www.zotero.org/support/word_processor_plugin_troubleshooting#zotero_toolbar_doesn_t_appear