here is a modified header.php to allow the use of an uploaded dashboard – appearance – header header image:
https://pastebin.com/7UCQm1Yy
(basically a copy the respective code from Twenty Eleven, section removed which would automatically grab the featured image in single posts or pages, included the existing title (logo) section as alternative if no header image is selected. – not tested with all possible theme options – particular the ‘Styling Settings’ options were left on default or empty)
adjustment of the image size in functions.php (you need to adjust that to the exact size for your design):
define( 'HEADER_IMAGE_WIDTH', apply_filters( '', 920 ) );
define( 'HEADER_IMAGE_HEIGHT', apply_filters( '', 155 ) );
adjustment to style.php, add this style:
#header img { width: 920px; height:auto; margin-left: 10px; }
you might need to adjust the position of the navigation;
for example:
.navigation {
right: 12px;
bottom: 8px; }
good luck ??