I need assistance in editing a wordpress navigation menu

General information for the website: Adaption of starter theme
Kind of development: Customization of existing website
Description of requirements/features: I have taken 'understrap' a basic stater theme and I'm working on customising the navigation to perform and position itself differently. I'm now 'lost' and need a professional to sort this aspect out.

It may be simpler to point at what I want and then ask for it to be put into 'understrap' - then you can work on it within your own environment and then let me have the understrap edited version?

i.e.
I would like to have the navigation of : http://jobcareer.chimpgroup.com/nextjob/
put into understrap (https://understrap.com/)

It is the fly in aspect of the dropdowns (at desktop)
and the tie in with the slick nav (mobile menu) button
and the display of the mobile menu as a block beneath the mobile button.

It is just this adaption that I need (for now).

I can supply understrap and the JC theme - as I have both.
Extra notes: