Purchase invoice with same invoice nos and value entered two time

I have entered a duplicate purchase in the month of April 18. We have also filed our GST returns. Kindly guide me to do settles this query. Correct purchase bill entered in the month of May 18. if i delete the purchase bill in the month April 18 stock is coming negative and also there will change in the figures of GSTR3B filed.

Kindly suggest easiest way to tackle this query.