Reference prior year based on prompt in Narrative reporting

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I have a client requirement where they want to select a year and period and show the comparison with the same period but for the prior year in the second column.

I created a column with a prompt for year and period for the input but I can't seem to reference the value in column in and offset it by -1.

It was simple to do in FR but I cant seem to figure it out in MR. Any ideas?