How to set headers in TN

I’m sending bizdocs to a Trading partner. If I use pub:client:http service and set the headers/Content-type as text/xml. The partner can recognize the post. Through tn I’m not able to set the http header info and due to which I’m getting the following error:

Failed parsing XML: The import has failed due to one of the following reasons: 1) Required data fields were missing; 2) There were invalid or nonsupported characters which may have been
introduced by external file editors; or 3) If this is an smbXML import, the elements may have been out of order as defined by the DTD. Premature end of file.

This error occurred on line -1 of the uploaded file.

I get the same error when I remove the header from the pub:client:http service.
I need to know the way to set headers info to send the bizdoc successfully.