I am very poor in math. How can I become a computer science engineer?

Weakness in maths is very common fear. But it’s root may be lack- of efforts or of proper guidance.
You need to overcome both of these. If you want to prepare for Engineering, then you need to give the JEE exams. For which you will have to join tuitions for PCM. If you go to the Institutes for a 1 or 2 year course then they will provide adequate knowledge required to cracked the Exam. But then at the same time, the student has to do a lot of individual work to succeed with it. Having joined an institute increases the work load of the student as the teachers there, cannot provide enough time to the individuals on their doubts(But the scenario is entirely different if you go to any premiere institute at Kota).
So I would better suggest you to find a local, but good, maths teacher who could ponder more time for your weakness in it.