1nA current is the input offset current, Right?. It is not a input bias current. why do we need to consider input offset current here?

No, input bias current. Specified at <±2nA, so 1nA is a reasonable value to take, considering how little effect it has.

 

1nA current is the input offset current, Right?. It is not a input bias current. why do we need to consider input offset current here?

Why do we not?
Its simple Ohm's law. The offset/bias currents must go through the input/feedback resistors causing a small voltage drop error.
So you need to have those resistors small enough that this voltage error is negligible compared to the other errors in the system.

Now can you stop throwing random things on the wall to see if they stick and deal with the trace resistance problems we told you about?

 

First step would be to tell us where you made the measurement. @pinkyponky, do you understand why that is important?