You can just edit the icon from studio module.d\

Install the Studio app:

Begin by installing the Studio app in Odoo.

Access Studio from the Sales module:

Navigate to the Sales module and click on the Studio module icon in the navigation bar.

Edit the email template:

Once in Studio, go to the Reports section.

Find and select the email template that you want to modify.

Change the icon:

Inside the email template editor, locate the icon you wish to change.

Make the desired modifications to the icon.