Gstr 3b reset button discontinued

Dear All

I am a small business owner (Services and Trading in IT with turnover of under 50 lacs) and have been learning and filing my GST Returns since the time it started.

I did a big mistake while trying to fill my GSTR 3B for Dec 2018.

I had a Input GST Taxable  Purchase (Local)  of around 9 Lacs   for this month and SGST and CGST of around  81,000 each for ITC. There was no Interstate Purchase so the Input IGST was supposed to be 0.

In a big blunder, in the Input Tax Credit - All Other ITC Page of Form 3B the  Taxable amount (9 Lacs) was entered insted of 0 for Input IGST. The SGST and CGST were entered correctly as around 81,000 for ITC.
While paying tax the tax amount of around 60,000  (IGST + SGST + CGST)  was set off against this IGST ITC of 9 lacs  that was entered by mistake. I was supposed to set off  the tax payable against the Cash Ledgers.

The Credit Ledger is showing a balance of Rs 8.40,000 (9 Lacs - 60,000 used) as Input IGST.
The amount to be paid is already paid and lying unused in the Cash Ledger (Around Tax 60,000).

Unfortunately the GSTR 3B is submitted and shown as submitted in Status. I have not yet filed the return.
I need to change the Input IGST amount to 0 from the incorrect Taxabale Amount of 9 Lacs that was entered.

I saw in some Youtube videos that there is a Reset GSTR3B Button, but I do not see it.
I spoke to the help desk and they tell me that it is not possible to make changes after it is shown as submitted. They told me that I will have to file the return as it is and reverse the wrong ITC in the next month's GSTR 3B.
I saw some youtube videos about making error corrections in the wrong ITC in the subsequent month's GSTR 3B.  But in those only an amount upto the amount of ITC of IGST for that month can be reversed. My figure is huge at 9 lacs to be reversed and I never have ITC of  other state (IGST). My worry is how will I be able to reverse if if I have no Input IGST ITC in future months. Will I be able to reverse it agains the Ledger Credit Balance of IGST ITC ?

I am not an accounts person and I do not want to get into trouble for this. What will be the best way to get this resolved.

Experts here please guide me on how to fix this as I am having sleepless nights.  Should I report the error to my Ward Officer. Will they be able to remove the 9 Lac IGST input credit entered through their systems ? I still have 7 days before the due date for filing this GSTR 3B Return for Dec 2018.

Thanks in Advance

Amit Kalra