You update email templates, by going into developer mode, got to Technical, Email Templates.

When you get to the content, it's really difficult to edit, and the doco shows a toolbar that is no longer there, so you can't see the code.

I found it by accident. Double click in the edit pane, and the toolbar comes up, and then you can see the code from the > symbol.

Short video showing this: https://app.screencast.com/SykkfoFdNOpPX