Hi Khushi (if this is your name), first, you need to set your priorities and objectives in life. Then, you need to ask questions of yourself before jumping to any conclusions.
I suggest you join there. You've got good reasons to do so if you analyze it carefully.
a) You are in BPO. You may not earn good experience as a trainer while being in BPO. You may not even get a chance to grow yourself.
b) You are a process trainer. You may be restricted to the same pattern/syllabus/course for months. As a trainer, you need to expand your wings.
c) You are getting a chance as AM - Training. You are getting growth in terms of designation and job profile. I am sure in terms of remuneration too.
d) You are opening a new door. You are getting a chance to experience a whole new world of working (BPO's work style is entirely different from any corporate body). I can say this because I've worked in both environments.
However, it's you who has to decide. So, make decisions after pondering over all the points.
All the best!