Formula to apply excess cash to outgoing payment

Hello,

I am working with a large runoff model that accounts for all incoming cash from business activities and all outgoing cash for the same for a period of 84 months, which end result is to calculated the NPV of the net cash.

I am trying to incorporate a formula that would allocate any excess net cash towards the prom note so this debt is paid down faster. However this is obviously resulting in a circulur reference error.

Does anyone have an idea on a formula to get this to work? I can't hard code the net cash number because the model is always changing and the hard coded number may change and not be relevant anymore. I have attached a sample with a few rows, let me know if any other details are needed.

Thanks for the help!