Hi,
Thanks for using our plugins I can help out here.
First, to resend the tickets the Order must be completed first and then the option will appear.
Is the order completed that is not showing the resend tickets in the Actions Dropdown of the Order?
I could not reproduce that error otherwise on my site.
Tickets Email
The tickets email css is inline so it is all in the template to edit.
The file you are looking for is found here:
the-events-calendar\src\views\tickets\email.php
Our themer’s guide can show you where to move that file to your theme to safely edit:
https://theeventscalendar.com/knowledgebase/themers-guide/
Let me know if you have any follow up questions.
Thanks