logo and Menu in single line

Yes, you can. Are you using the social media icons on the right side of the logo? A link to your site would be helpful, but basically we need to add some Custom CSS. (Not sure if this theme has a Custom CSS area or not – if not, use a plugin)

.themonic-nav {
  float:right;
  width: 50%
}

Of course, you will need to tweak it to fit your needs.

Hope this helps!

which plugin to use for this

I haven’t used it myself, but I think something like this would work:
https://www.ads-software.com/plugins/simple-custom-css/