Board Thread:Support Requests - Designing Your Wikia/@comment-27958477-20160418232424/@comment-856287-20160418235648

If chat is enabled, it should appear on the navigation bar automatically—pages may be cached by your browser, but should update soon. I would just wait, maybe clear the browser's cache.

Otherwise, you could edit MediaWiki:Wiki-navigation on your wiki and add a link to Special:Chat, but you shouldn't need to do that. Just be patient.