Amendment to tax invoice

1. my sales invoice for the month of aug-19 taxable value was 1,00,000 & gst amount was 18000 & paid to govt.

after that in the month of Oct-19 I came to know that invoice value was 90,000 & gst amount was 16200

now without raising credit/debit notes,
I like to amend bill in the month of Oct GSTR1 then where that differential tax amount showing/ where it will be adjusting.