In BlueSpice you have a second navigation at the top of the page. This area is named TopBarMenu. Wiki and blog are set and linked by default but as an administrator you can set different internal or external links. It is also possible to structure links as a dropdown.
Open the page „MediaWiki:TopBarMenu“ and enter names of internal wiki pages or external links.
This is how you build up the links:
URL can be a name of a wiki article or an external link.
* Blog|Wiki Blog
** BlueSpice Blog|https://blog.bluespice.com|BlueSpice Blog
** Hallo Welt Blog|https://blog.hallowelt.com|Hallo Welt Blog
In the wiki admin preferences at the section „menu customizer“ you can define e.g. the number of nested layers.