How do I prevent my header from changing when the screen gets smaller?

I’ve installed a WordPress theme where the menu items of the headers go onto multiple lines when the screen size gets smaller. Only when the screen gets too small, it goes to the (mobile) hamburger menu (see image 3). Firstly it goes onto 2 lines and then 3 lines. Does someone know how to fix this issue? I only want it to stay onto 1 line or that the hamburger menu appears when it doesn’t fit on 1 line.

Thanks in advance!

I don’t really know how to fix this.