Gadget export
To export the site gadget, click on "Download" button, save the downloaded file, go to Special:Import on destination wiki and upload it. Then add the following to MediaWiki:Gadgets-definition page:
* site[ResourceLoader|default|peers=site-styles|dependencies=mediawiki.util,ext.gadget.site-styles]|site.js|NavFrame.js
You must have appropriate permissions on destination wiki (including the right to edit system messages) and import from file uploads must be enabled.