Hi @MrSurajKumar,
I believe you're correct that the Teacher App will not let you add people. The Canvas apps have a lot of functionality, but do not have every feature/capability as Canvas on the web. The Canvas Teacher Mobile Features - Instructure Community - 388744 page gives an preview of functionality the teacher app supports and does not support. You should be able to use the browser on your device to do most of the things you can't do in the app though.
I would suggest you ask the Canvas team/admin at your school about adding the student, as I'm a bit confused by the question. Your school may restrict what you can do in Canvas and may need to do the addition for you.
I hope this info helps!
-Chris