Hi Alberto,
You are actually have 4 columns in the header including the site description, you could give this CSS a try, but I might not work work in smaller screens. I would recommend to add the site description into the logo image.
@media (min-width: 769px) {
.inside-header.grid-container.grid-parent {
display: flex;
flex-flow: row wrap;
}
.inside-navigation {
display: flex;
}
.site-logo {
order: 1;
width: 30%;
}
.header-widget {
order: 3;
width: 20%;
}
p.site-description {
order: 4;
margin-top: -20px;
}
nav#site-navigation {
order: 2;
width: 50%;
}
div#primary-menu {
margin-left: auto;
margin-right: auto;
}
}