I am bihar board student. 

Hello, Prabha

I you can give improvement exam , but for 2019 it's too late form date is expired in November, if you wish to give in 2020 ,you  have to wait now , the expected form date is always in mid of November this year so it long way ,and you have to wait , you can fill the form on the official website of cbse .

Hope this will help you!!