GuiBox Object - How to count rows indexes

Hi , Im trying to find a way to count the row index within a GuiBox Object. For instance I´m using T-code FF68

Each column have  an unique index  [ i ,0] Amount ; [i,15] Check no ;[i,26] Issue ..etc .

and  the Row index start with 0 and ends in 24 = (25 visible Lines only)

My problem is that I need to input hundreds of lines using an excel application where i = 3 To Last Active Row while in the GuiBox Object I can input 25 rows only  then  Index needs to be set back to 0 again time after time.

.FindById("wnd[0]/usr/sub:SAPMF40S:8000/txtFEBSCA-KWBTR [" & i - 3  & ",0]

Is there a way to count the Row Index within a GuiBox Object so I can use this value to set for example  an If statement

If a = 24 Then (To include 25 lines again)

.FindById("wnd[0]/tbar[1]/btn[5]").Press

.FindById("wnd[0]/tbar[1]/btn[5]").Press

.FindById("wnd[0]/usr").VerticalScrollbar.Position = 25

If a => 24 Then n = 25 To set the row index back to 0

[" & i - 3 -n & ",0]

Here is my code

Thanks in advance

Kind Regards

Alan