You are not required to apply for the additional days separately, just keep submitting applications as you have done so far. The person handling your application will automatically check your entitlement to the additional days, once the 500-day maximum period is full. You will not receive a separate decision on the additional allowance days. On the payment notification, as well as the status page of eService, you will see that the number of the paid days exceeds 500 days.
For more information on the additional allowance days, please click here: Duration of allowance payments – Additional allowance days