Hey Butti Nandini,

Start preparing for Bank exams during B.Tech, if you start preparing from B.Tech then it will be easy to you write exam immediately after the completion of B.Tech.

And the books for the prepartion of Banking are given below! Kindly go through them,

Quantitative Aptitude by Arun Sharma
General English by SP Bakshi
A Modern Approach to Verbal & Non-Verbal Reasoning by R.S. Aggarwal
current affairs, newspaper, magazines

These are enough for the preparation of banking exams! 

All the best!