You can account for any change in consideration, including increase or decrease in purchase and sale price, with GST in debit or credit note.
(A) : Increase in Purchase Price in GST using Credit Note in Tally.ERP9
To record an increase in assessable value for purchase :
1. Go to Gateway of Tally > Accounting Vouchers > Ctrl+F8 (Credit Note) .
2. Press Ctrl+V for voucher mode.
3. Enter the Original invoice no. and Original invoice Dt. of the purchase against which you are recording the increase in assessable value.
4. Credit the party ledger from whom the original purchase was made, and enter the amount including GST.
5. Debit the purchase ledger.
6. Select the stock item against which the increase is being recorded. Enter only the increase in assessable value without the quantity, as only the differential amount has to be paid.
7. Debit the tax ledgers.
8. Press Enter to save.