Hey!
I don’t know if you still need an answer but i faced the same problem today.
You could edit the style.css in the theme folder and search for
#colophon .site-info {
font-size:12px;
float:left;
width:420px;
padding:8px 0;
}
Edit it like this:
#colophon .site-info {
font-size:12px;
float:left;
width:100%;
padding:8px 0;
}
Be aware, that if you run updates, the changes could be overwritten. The better way is to make a child theme. Also i havent tested if this impacts the functionality of the theme in case of screen resolution of devices.
EDIT:
I created a child theme, copied the footer.php into the child theme folder. Made this edit on line 18:
<div class="site-info fixfooter">
(Added a class)
Then i added some CSS to the style.css in the child theme folder
.site-info.fixfooter{
width:100% !important;
}