Repeating groups: Reference to other textboxes in the same cell and textboxes in different cells


I need some help with a repeating group:

I am building a loan management tool and I have one page for the user to track each of their loans, including all the payments that have been made to it, the accrued interests of each period, and the outstanding balance for each period, as well.

I have advanced very well building this, but I have been stuck on how to refer to other text boxes in the same cell of the repeating group and to other text boxes in different cells of the same repeating group.

For example, each cell of the repeating group is a period (Columns: 1 | Rows: the number of period since the beginning of the loan to date), and each cell (period) has the following information (as text boxes): Cutoff date, Total Payments (during the period), Accrued Interests (during the period), Principal payments (during the period) and Outstanding balance (at the end of the period).

All the information is being extracted from two datatypes (loan details and payments). I have been able to build the first two textboxes of the repeating group (Cutoff date and Total Payments during each period) but I am stuck in building the remaining information needed for each period. What I need, for example, for the accrued interests is to refer to the previous cell’s outstanding balance and multiply it by the interest rate. I have tried for many hours to get referenced to the previous cell’s outstanding balance textbox without being able to accomplish it. Also, I have read a lot of posts in the forum that have similar solutions but not exactly this.

I really appreciate it if someone could help me with this. To be clearer, below is a picture explaining what I need to do (marked in light red) and what I have done so far (marked in green). Also enclosed please find a very simple excel with the formulas as a reference. Thank you in advance:

Excel file →!Ak6HoHEnzCuMg4EYyZhJBBZp-8UEcA?e=i8Fqm5

Try this plugin:

Thank you!