How to add/change HTML fields in Maintain Email Templates App

Dear,

I am facing problems changing an Email Template with the Maintain Email Template App in S/4 HANA 1809.

See attached screenshot: seems there only a (huge set) of STANDARD Sales order fields available.

However, I want to add the first and last name of the Contact Person that is in my Sales order as a Z-Partner Role on header level. This Z-Partner is also the Recipient in my Channel EMAIL.

Does anyone know if and if so how this is possible?

Best regards, Bart

1.jpg