Want a Nav menu in one line

Sorry for a very beginner question.
I’m trying to make a page with multi-languages, using the plugin Multisite Language Switcher.
There is an additional plugin to have the switch (national flag+language name) fit in the navigation menu, it has worked but somehow the switch went into the second line, and I can’t find any function to resolve this in the wordpress dashboard.

My website is https://kicf.koyukai.info/.

Would someone please point me where I should go to fix this, or is it impossible to have the menu in one line?