Details are lacking, but perhaps this will do what you want.
When a cell in column-R on sheet1 is selected (no changed), it make the cell in column-AA of sheet2 have a value of "No", using the same row as the selected cell.
This code must go into the worksheet module of Sheet1.
Note: sheet references are sheet code names, not worksheet (tab) names.
If this is not what you intended, then state your requirements more precisely and with more details, or upload a sample workbook that shows the desired results.
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