Hello,
It is not at all necessary to reappear for board exams if you want to reappear for jee advanced. But if you feel your 12th score isn't good, then it is upto you.
Good Luck!

Hello

no you dont have to give boards exam again just prepare for your JEE exam for next year if you are dropping a year, if you are giving an improvement exam for boards then you again have to give boards exams. Also you have to again appear for JEE Mains then for JEE Advanced for next year.

Hope that helps