Hi You must submit your file. Ico in the root of your website. Then you edit the file container. tpl of the page where you want your favicon to appear and you write this:
<link rel="shortcut icon" href="/your ico.ico" />
see an example in the container.tpl original of quick cart v3.5
<!-- BEGIN HEAD --> <?xml version="1.0" encoding="$config[charset]"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="$config[language]">