So, first of all iam assuming you know about the syllabus for KVPY SX 2019-2020 properly
Physics:- it is the most important subject in KVPY SX, remember there will be few questions from modern physics part (app.4) and most importantly the graph based questions. You have to master the graph based questions, if you are beginner follow hcv, else atleast 4 questions daily from IE irodov and ss krotov specially you have to be a clear concepts in mechanics. I read in your thread that you are weak in mechanics my friend if you are cracking KVPY SX you should have strong hold in mechanics especially the newtonian.
Give much importance to heat and SHM and try to make self formulae from them. Do regular questions on SHM like time-based and amplitude and most importantly the phasor diagram and graph.
Again I am saying don't skip the problems with graphs in mechanics and SHM.
Ok in case of chemistry don't take tension just follow NCERT and you will be rock in the exam but you have a clear concept in organic some silly reactions and I hope you are doing n awasthi book. That's enough.
In case of mathematics you have a clear concept in co-ordinate geometry mainly the conic section since when I gave KVPY atleast I got three questions from conic sections all were interesting. And you need some special inequalities in your mind if you don't know I will give you the inequalities that is par from jee syllabus. And if you are preparing hard for Jee you can tackle the math of KVPY but remember if you don't know the inequalities please tag me I will give you.