Dear aspirant

There is nothing can be done in this case.

You will have to go and attend the exam on the centre you have been allotted and whichever City that is.

Actually prefer city is given on the basis of candidates preferred that city and no. Of centre in that particular city. If the centre got filled,you may be get allotted in other city centre also. It's just optional choice they ask during application form. It's totally depend on the availability of centre and no of candidates preferred that.

Once admit card is out and centre is allotted,you can't do anything much. You might have put city name which where preferred by most of the students and you might have filled your application form late which led to exhaustion of seat in centre of that city.

Now you can only do is that you should plan how to reach centre and give your exam.

Hope this information helps

All the best