Setting a custom favicon for my site

How do I update the favicon used with the Simplify theme?

Currently, there appears to be a black dog with a red collar shown as the favicon when I view my home page (static page). But when I view my blog or other pages I have created, the favicon image just looks like a blank document.

I’ve searched through all the PHP files to see if I can change it myself but nothing is jumping out at me. I have also browsed all the image files that come with the Simlify theme and I do not see an image with a black dog and red collar.

thanks for any info you can provide.

p.s.
(I’m aware I can download a plugin for the favicon, just want to know if I can manage it through the theme).