GST Excess Amount Paid And Credit for it Electronic Credit Ledger-Regarding

Respected CCI Members,

My Query is relating to time period within which Excess gst paid reflected in electronic credit ledger.
Actual Problem is My friend erroneously mentioned inward supplies as outward supplies and erroneouly mentioned amount of Outward GST payable as Input Tax Credit while filing GSTR 3B for the month of august 2017.Due to this error, he needs to pay tax through cash.But Actual position is if it is correctly filed, excess input tax credit available.
please clarify following query in respect of above thing.
Due to error only, assessee need to pay tax through credit as well as cash. Can we rectify this error by submitting gstr 1 and 2 correctly?
2)After Filing of gstr 1 and 2, how much time will it take to get credit of excess of amount that we paid?

Kindly Help me in this regard


Thanks

Dhebek.M.N