Hello!
Since your percentile in JEE Main is below 40, getting seats in the top government colleges is very unlikely. For the 3rd round of counselling, you should focus on state level private engineering colleges or less competitive institutes that accept lower percentiles. You can check the JoSAA or your state counselling website for the list of participating colleges and their opening and closing ranks for previous years. Using this, you can identify colleges where your percentile may give you a chance, though options in government colleges will be extremely limited.