Hello,

There will be no change in syllabus for supplementary/ improvement/re-exam. You have to prepare from the same syllabus. if you find difficult to cover it all then cover long questions from all the chapters.  every chapter has 5-6 long question which holds more than 10 marks. do read them. remember them no matter what.

cover short questions from chapters which you find easy. get sample paper or solved question set for your failed subject. practice that whole book. don't even leave a single line.

practice questions as much as you can. solve your academic book if you can.  put your efforts now to clear the paper in one go. if you have to give more time then do give and study. it is not  good to hold back paper in 12th. it will waste your time.

Hope it helps!