GST Wrong Input

kiran (accountant) (444 Points)

28 June 2019  
A ltd have two unit one in nagpur & another in Indore .
B ltd in indore is supplies goods of both unit
if b ltd raise bill on A ltd nagpur unit with IGST but by mistake bill book in Indore unit & take igst input in monthly return this error found after two months.

how rectifying this mistake.