How I can complete my B.Tech while I'm doing a job in the private sector?

You can get good private college. But, now a days, getting into a college is not important thing, important is which branch you choose. Computer Science and Automation and Robotics are two branches having great scope in future. I would suggest Gulzar Group of Institution for these two branches, as G

Focus on your studies first. You can teach in any coaching for evening shifts that will help you to earn 10k-15k per month.