I have completed a 3-year Diploma course. Can you suggest some government colleges that I can get for B.Tech?

As you have Diploma you can apply in engineering college from 2nd year through lateral entry, but for that you have to clear JEE mains with a good rank.

IITs and NITs are government backed colleges but you need IIT JEE score and science background. You can try for VJTI as well as it is having the best ROI and great placements.