Hi there @khushboosinha ,
Did you insert the back tower correctly? as shown in my image below?
Carefully connect/press the tower into the plate, leaving no gap.
If you think it’s really not that easy to assemble both parts. Lay the back of the tower on a flat surface and try to insert the base plate into the right place slowly, straight, and gently downward with a controlled force.
You have to do just like the image below!
Best Regards