Apologies, but there’s no feature for that. The widget does not allow for any kind of link at the bottom of it. It’s just the listing of posts.
Technically if you wanted to change how the themeblvd_get_mini_post_list function works (which is what the widget pulls from), you could copy it to your Child theme’s functions.php before the framework runs to modify it, but keep in mind this is a code customization you’d need to make to the theme. You can find this function in /framework/frontend/functions/parts.php in order to copy it.
Here’s information about editing theme functions: http://dev.themeblvd.com/tutorial/editing-framework-functions/