Hello Mhd Abbas,

I don't understand the purpose for which you are doing this, but you can definitely do this. The only thing is you will have to register yourself again with the board of council, i.e. ISC, CBSE, or any other state board. You will have to complete your 11th and 12th again with Biology subject, and most probably the two years in which you studied Maths, will be represented as drop or an academic gap. There are chances that you will not be able to apply certain graduation entrance exams, because of the age restriction. Well this is not the case with exams such as JEE and NEET.

Most people consider NIOS, i.e.  the National Institute of Open School, for re registering.

Hope this Helps

Regards

Hello student if you have done your class 12 with maths once and if you fail in it or not satisfied with the result then you can only appear with the subject you have studied 2years in your school if you want to change your subject then you have to start with class 11 again. Please help me with your board of education whether its  cbse icse or state board so that I can provide you exact information

Feel free to comment if you have any doubt

Good luck