Adding items to the right Index record

[Ben_Entrew]

Hi all,
try to assign a value to the right index.
I got one table called months with three columns:
Reporting_Month,Forecast_Period, ID

I set two indexes on the column ID and Reporting_Month, where the Datatype of ID is AutoNumber.

Basically I want to add to the reporting month = 092013 the 12months forecast value 102013-112014 in the same months table record.
How can I do that?

Thanks in advance.
Regards,
Ben