Header image needs to be aligned as LEFT

Try adding this to your custom CSS:

#masthead .header-image {
   float: left;
}

.site-navigation {
   clear: both;
}

Where can i find custom CSS?

I can see three things in my editor;

style.css
editor-style.css
rtl.css

Try installing a custom CSS plugin.

Thank you WPyogi & esmi

It worked!

Thanks a lot.