Please apply following css code to Appearance > Customizer > Custom CSS

You can play with the paramater.


@media only screen and (max-width: 768px) {
.site-branding {
background-position: right right !important;
background-size: 816px 744px, cover;
}
}


background-position :

http://www.w3schools.com/cssref/pr_background-position.asp

backgound-size

http://www.w3schools.com/cssref/css3_pr_background-size.asp

Example :


@media only screen and (max-width: 768px) {
.site-branding {
background-position: center center !important;
background-size: 1090px 727px;
}
}