my subject is commerce, but now i want to go for civil engneering tell me how can i do that

you can opt diploma in civil engineering on the basis of your 10th and after that go for B.Tech this is only way for you.

There is no way to do Civil engg unless you go back and take PCM subjects, which does not seem to be feasible. The best alternative for you would be to join a Contractor engaged in civil engg works, learn the nuiances of the job there and then proceed in that field on the basis of the skills acquire