When you say Site Link - I assume you mean the Logo?
Only way to do this is to try editing the theme - likely the index.html file. There’s an old thread: Website logo linked to home page URL. How? - #10 by andrea where the following from @bobafifi worked: Look for something like…
<!-- Site Logo -->
<div id="logo">%logo%</div>
and change it to
<!-- Site Logo -->
<div id="logo"><a href="%base_url%">%logo%</a></div>
However… I would strongly consider switching to a newer responsive theme - Caribou is NOT mobile friendly. Some newer themes will do what you want automatically. Other ‘blank’ theme / frameworks (using Stacks) enable you to add your own logo where you wish and link it as you would link anything else. Remember, if you do the above it is possible that an update to RW will overwrite your edits.