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There is no 'automatic' way of doing that. There is no block you can use to display the Link Categories. What you need to do is to create a custom block and have it displayed on top of your forum (a.k.a. NewBB module). This would display the custom block on all pages of the forum.
For the pages to display only in the Forum index page, you might need to edit the newbb_index.html file in your template set and 'hard code' those link categories into the file.
Please do experiment with the admin functions and search the forums, especially about custom blocks and editing templates.
Thanks!