How to keep menu on one line?

Hello,
I am currently working with the THBusiness theme that I really like, but I encountered some issues with the menu.I have checked all the previous topics but none helped.
My menu is currently displayed on two lines, while there is plenty of space on the left. I would like to have the menu one one single line.

Here is a screenshot (my website is currently not on the web)

I have tried editing the css code in various ways (btw I am using a child theme) but without any result. I am a beginner in css and wordpress in general.
Therefore I want to know
– how do I reduce the left margin to fit the menu on one single line?
– is the header logo responsible for this ? (i.e. it would take a space that cannot be occupied by the menu ?)

Please note that I have installed the polylang plugins which creates a primary menu for each language – in my case I have 4 main menus. Maybe this impacts the size of the menu ?

Thanks for your help !