See by internet research , I don't find out any official document that can instruct what syllabus you should follow.

But probably you will have to follow the new syllabus as I have heard from other sources. I would like you to contact to your teachers with the same questions and I am sure they will give a insight about it.

Have a great eve!

Hello aspirant,

Since you have failed in 12th board in 2019 and wants to reappear in the exam, so it is suggested to follow the present syllabus as the questions will come from the present syllabus, not from the old syllabus. Prepare the subjects and make notes accordingly. The old syllabus is not valid if you are reappearing for the 12th board exams this year.

Hope, it helps you.