Treatment of sales return in excess of sales in ap vat

Can any body help in this peculiar situation?

In Andhra Pradesh VAT how to treat Sales Return when sales return in a month is in excess of Sales for that particular month? The AP VAT online portal does not allow you to enter negative sales figure in a particular month. ( In Karnataka VAT portal you can enter negative sales figures)

I can think of  some solutions:

1) Treat sales return as purchases and claim vat on sales return as input credit ( ofcourse this is wrong)

2) Enter the sales figure as NIL and claim the balance in next month ( This too is not correct)

3) Revise the VAT returns of earlier months for which the sales return pertain to.

Any expert opinion please?