Dear Muskaan, after the exams, you receive your marks list. And then it is too late to make any changes. And your admission into 11th standard will be based on your 10th data. So it will be complicated. So its always advisable to make the changes before the exams. 

Hello,Muskan

Well you have to contact your school office ,from there it will be possible otherwise CBSE board office but go to school official they will do that may they ask for application or whatever or they will give you better solution ,so don't worry stay calm.

All the best