Ammendmend in gstr-1

CA Piyush Shivani (...) (137 Points)

07 October 2018  
two b2b invoice of march wrongly entered as b2c . out of one is noticed by me and i rectify the same by entering such b2b invoice in july 2018 gstr-1 correspondingly i reduces the amout of such invoice in b2c colloum for march. which is totally ok.

But now for the second b2b invoice i am trying to reduce the b2c amount for march once again in sept 2018 gstr-1 but portal doesn't allow me by showing an error " ammendmend already had been done in previous month"
now please guide me what to do.