Can't add widget to certain sidebars

Hey there,

I need help adding a widget called ‘revolutionary slider’ under the navbar.

Some background info:
I’m completely new to wordpress. The website I’m working with isn’t made by me. I normally do graphics design for my employer, but he gave me the opportunity to work on and maintain his website. I do a lot of programming work myself in c#, and knowing that wordpress is for everyone (even for people with no experience in web development) I gladly accepted.

As I started, the first thing I did was update the plugins and theme. This wasn’t a great move, since I found out that the guy before me actually changed a couple of things in the css directly in the theme files instead of in the custom css tab. I’ve been trying for hours to get the slider back under the navbar, without result. I decided to learn some basics of css.

Now, to get on to the point:
website: https://www.kachelbouwer.nl
Theme used: pinboard.

As it seems, pinboard has 10 sidebars. But in the customizer, I can only add the widget to 3 of them: the header (apparently only intended for ads), the footer and the wide footer. Trying to add the widget to any other sidebar through the widgets tab results in no change at all. I have no idea why it differentiaties those 3 sidebars from the rest. I guess I’ll have to change the css in such a way that sidebar called ‘sidebar top’ is available for widgets.

Sorry if my post is incomplete, this is my first post. If you guys need further information please tell me. Any help is appreciated.

Thank you!

https://www.ads-software.com/plugins/css/