Hello Hanumath,
I am confused with your question, does DMT mean Data Migration Template?
If yes you will have to choose the migration template to extend, (more confused since you extend Inbound services for this.) Refer the below blog.
Add extension fields under the Migration template from SDK
Then you also said, you have downloaded them long back. If so hope you are using the templates downloaded after extending it with your extension fields. If you have not, you will have to download the template after you have added the new extension fields in it.
Hope this what you want to know, if not kindly elaborate on your requirement.
Regards,
Chandan