I can understand your perspective that you are looking for an advanced personal trainer certification because you already are a physical therapist.
However, the requirements on a personal trainer are usually very different from those for a physical therapist. Unless you have an interest to work with people after they just left physical therapy, you will be required to develop exercise programs for healthy people who want to be challenged in a variety of ways, both for weight training and cardiovascular exercises but also flexibility and balance. You will need to know how to progress them, and I doubt that this is the object in physical therapy.
Since you are in India, I would suggest that you take a look at the NASM international personal trainer certification. Here is a link: http://www.nasm.org/personal-trainer/international-cpt