Hello dear,  it is impossibleto prepare for jee mains in one month without have a good knowledge about class  11 and class 12 topics. In month you should  practice mock tests and previous year papers in time frame. I am providing the chapters that you should more focus on this -

Maths-

Coordinate geometry 

Definite integrals(calculus)

Linear algebra and complex no 

Permutation and combination (assured question )

Chemistry -

Inorganic (complete ncert) 

Organic(named reactions) 

Physical ( equilibrium, thermodynamics, mole concepts, kinetic theory of gasses) 

Physics - 

Practice DC pandey and HC VERMA questions 

For more topics you can prefer the following link

https://engineering.careers360.com/articles/jee-main-2019

Hope this helps.