Move to diferent cell using date as reference

I’m new in excel and I hope this is the right forum.
I have a collection report spreadsheet and in the cell B4 I have the date of the sale, and B5 the amount of debt, and in cell B6 the debt between 0 to 30 days, B7 31 to 60 days and B8 61 to 90 days, and B9 90 days and above. How can I do to move automatic the debt to the next column when is getting older

Thanks