Hii

First of all you need not to feel low or loose hope. Remember you will achieve your goal if you want it with all your heart and are honest towards the path you are following to achieve it.
Since you would have studied already for JEE Mains, So it must be easier for you to study the same concepts for the second time. 
I would suggest you to first try solving a paper so that you can check where you are lacking. 
Once you know your weaknesses then you can start to work on them.
So now you have 2 months more for your preparations. Start with basic concepts and make sure you clear all the concepts and have a strong hold on basics.
Refer to NCERT books for basics.
Solve the questions regularly and make sure you check the question by the end of the day and see what you are missing.
Do not focus on things happened in the past, forget about the January sessions low score and concentrate on what is in front of you.
Be dedicated, work hard, stay confident.
Use proper study material for your studies and keep solving sample papers to improve your preparations.
Here is a link which will give you list of the books you can use for JEE preparations.
https://engineering.careers360.com/articles/best-books-for-jee-main-2019

Do not think about other things for the next 2 months, and work only and only on your preparations.
Do not go on reading just the chapter rather solve questions topic wise and understand what you study.
Do not rote learn things and yes note down all the formulas and byheart the formulas and facts. Keep them handy for last minute revision.
STAY CONFIDENT and DO NOT LOOSE HOPE

Thanks!!

You have plenty of time for 2nd phase jee mains exam .First of all go through each and every formula of scoring topic and scoring subject.You should start with chemistry, especially from physical and organic chemistry.and at last inorganic.Then you should shift to physics afterwards mathematics.Revise all formula as possible.Then solve previous years paper of jee mains.This will boost your marks in jee mains.Keep faith on yourself.

You can ask if you have any other queries..

BEST OF LUCK!