Follow By Email Blog Subscription – Changing Email Icon

Hello,
I have recently implimented a follow this blog feature in my clients website http://www.detailsfullserviceinteriors.com/. When a user subscribes to her blog they will receive an email with the blog post so they can stay up to date.

They recieve an email like this:
http://www.detailsfullserviceinteriors.com/wp-content/uploads/2016/09/IMG_6210.png

What my client asked me to change is this icon to her logo:
http://www.detailsfullserviceinteriors.com/wp-content/uploads/2016/09/IMG_6210-copy.png

I do build websites for a living and this is pretty urgent so please when responding do it step by step.

I am an avid web designer and know a lot of coding if that’s what has to be done.

I’m just hoping it’s a quick fix.