In the first correction window, Candidates were able to change their Examination centres. Now, if you are not able to make any corrections to the Examination Centres, it might be because you already used the correction window again for the 2nd time. If you already availed the correction window again that also is a one time correction facility which means you can use it only once and you have to make all the changes that you need to all at a time. You cannot use the correction window for one edit at a time. So now, you have to be contended with the Exam centres you initially chose along with the medium of the paper. Unfortunately, there is nothing that can be done.