What should I do after completing Diploma rather than engineering line?

You can go for IT organizations, fashion designing, painting companies etc. Water supply, HIL, BHEL, Communication services, BCPL, Railways. Pursue a certificate course from A. M. I. E (Associate Member of the Institutions of Engineers), you can also go for NIFS. Best of luck.

If you are in diploma field, then you have to take any field is that only engineering/B.Tech. Rather, if you don't want to, then go for government exam preparation to pass out exams like JE (junior engineer), etc.

You always have government jobs open for you. Have a look on those.