Hi Shaikabdul, the way the counselling procedure works is as follows:

You have to arrange colleges in decreasing order of preference. The algorithm starts checking your list from the top (which should be your highest priority) and traverses down and locks at a college you are eligible of with your rank. The list of colleges below your locked choice gets disabled and you can't get admission in one of them. If you appear for a second round of counselling, the algorithm runs again from top and scans down the available set of colleges till your locked choice.

Now, in case a seat gets empty (for whatever reason) in a better college in the upper part of your list, you will have a chance to get promoted and secure a seat in that college (only if you are eligible). If not, the algo will keep running and lock at the same college as the first counselling.

So, you will have a seat at the end of everything, you need not worry about that. To appear for the second counselling, you have to check the "appear for second round" section while visiting your reporting centre (or tick-check the option if you're going through an online counselling) and wait for the second counselling results.