Run code on any selection from validation list

Hello all,
I have a long piece of code currently attached to a button, but I would like to code to run whenever a selection is made from the dropdown list in cell C4 in the 'Feedback' sheet. The code starts

Sub mcrpasteformulaandcommentlist()
    ActiveWindow.SmallScroll Down:=23
    Range("C50").Select
    ActiveCell.FormulaR1C1 = _
        "=IF(R[-43]C[1]=""y"",(CONCATENATE(""Well Done "",LEFT(R4C3,FIND("" "",R4C3)-1),"" you have completed "",R[-43]C[-2],"" "",R[-43]C)),IF(R[-43]C[1]=""n"",CONCATENATE(""Please use the "",R[-43]C[-2],"" user guide to complete "",R[-43]C),IF(R[-43]C[1]=""I"",""Teacher Comment Required"","""")))"
    Range("C51").Select
    ActiveWindow.SmallScroll Down:=-36
    Range("G7").Select
    ActiveCell.FormulaR1C1 = _
        "=IF(RC[-3]=""y"",(CONCATENATE(""Well Done "",LEFT(R4C3,FIND("" "",R4C3)-1),"" you have completed "",RC[-6],"" "",RC[-4])),IF(RC[-3]=""n"",CONCATENATE(""Please use the "",RC[-6],"" user guide to complete "",RC[-4]),IF(RC[-3]=""I"",""Teacher Comment Required"","""")))"
    Range("G7").Select
    Selection.AutoFill Destination:=Range("G7:G26")
    Range("G7:G26").Select
    Range("G7:G26").Select
    Range("G8").Activate

there is more code after that but I couldn't insert it here. Is there a prefix or coding for applying this to the validation list selection?

Many Thanks!

Luke