Remove cumulative total

Hi JurriaanQEL

Please see the attached file here.

Hope this helps. Here are the steps I performed

As you said we need an assistant field to undo the Cumulatives. So
First I created a "Parameter Table" to get "month number" in our Main Table

Then we can use this Calculated Column to get Monthly figures

Monthly Figure =
VAR PreviousMonthValue =
    CALCULATE (
        SUM ( Table1[Cumulative] ),
        FILTER (
            Table1,
            Table1[Year] = EARLIER ( Table1[Year] )
                && Table1[MonthNumber]
                    = EARLIER ( Table1[MonthNumber] ) - 1
        )
    )
RETURN
    Table1[Cumulative] - PreviousMonthValue