User By mistake put Gst tax on Prepayment invoice:

Hi All Experts,

We have a Standard invoice with amount 51,000 and we apply two prepayments on it first one is 49,000 and other one is 2000. On prepayment amount 49,000 user wrongly put 17% Gst on line  rather then put this Gst tax on item line. After this tax is calculated on 49000 with amount of 8330.

Would you please assist me how we can resolve this issue.

Regards

AYAZ