excess ITC taken in GSTR3B in July. How to reverse.

Arun Garg (Slf) (41 Points)

19 December 2017  
We have entered value of purchases instead of Tax (ITC) in col. IGST credit in GSTR3B return of July 2017.
How we can re-adjust/reverse the excess credit.
There is no option to re-open the return after the filed option exercised.