Add a menu to a Wordpress theme

I have a navigation menu, used on another website that I want to add to a Wordpress theme. I don't need to access the menu in Wordpress / add it as a widget / or add/remove in the backend etc. - it just needs to be referenced (and appear) on the Wordpress site - so hopefully coding into the theme. 

The Wordpress theme is a custom / paid for theme (already owned). It has a general minimal look/structure and already has a side menu, that I also want to use/keep.


The menu to add is a fixed/sticky top bar menu.

 The menu is used on another website and is referenced in that other website (non Wordpress) so it can be edited outside of either website, and easily updated across the various pages/websites. I have no knowledge of Wordpress theme creation / editing. But assumed the same could be done with the Wordpress site. 

Let me know if you need any further information.

A mock-up of the Wordpress page and the menu to be added is attached a a jpg image.


Thanks in advance