You can process existing orders if they are no older than 60 days. Select the orders you want to sync on the Orders list, open More actions and click on Process in Exporteo.
You can add an
<img> element linked to the logo image hosted on your website.
<img src="https://website.com/images/logo.png" style="width: 200px">
If you have your logo in SVG format then you can insert it directly as an
<svg> element in the output template.
You can switch to the preview mode to check if the logo looks good.