This is quite easy! You can do this by following the instructions below:

  1. First, be sure that your company logo is in a publicly accessible location, if it's on your website, you can simply click "Copy image address".
  2. Head over to your email templates or your page templates (or both). 
  3. Find a good place for the logo, then paste in the following code:

    <img src="THEIMAGEURLYOUCOPIED.PNG" style="max-width: 250px; height: auto;" />

Replace the values in the code examples above with your actual site URL and the URL of the image you copy.

The following video can also help you out: 

The FetchApp support team is always happy to assist with this request, so feel free to reach out at for assistance.