How to edit SW-Mail-Template-Detail Page

I’m looking to add a custom field to the page, but sadly sw-mail-template-detail.html.twig is not a component. Its placed in the page folder from sw-mail-template.

The only components in this folder I found are sw-mail-template-list and sw-mail-header-footer-list

So how can I edit the page without having a component? Cant find anything in the docs