How do I have excel add an drop down list if the cell before it is populated with text?

Private Sub CheckBox1_Click()

If CheckBox1.Value = True Then
    
LC = Sheets("Run Table").Cells(1, Columns.Count).End(xlToLeft).Column

    With Range("D8").Validation
        .Delete
        .Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _
        xlBetween, Formula1:="='Run Table'!$A$1:" & Cells(1, LC).Address
        .IgnoreBlank = True
        .InCellDropdown = True
        .InputTitle = ""
        .ErrorTitle = ""
        .InputMessage = ""
        .ErrorMessage = ""
        .ShowInput = True
        .ShowError = True
    End With
    
     Range("C8").Value = "Select the column in your run table that corresponds with resin type"
     Range("D8").Select
     SendKeys "%{DOWN}"
     
Else

    With Range("D8").Validation
        .Delete
        .Add Type:=xlValidateInputOnly, AlertStyle:=xlValidAlertStop, Operator _
        :=xlBetween
        .IgnoreBlank = True
        .InCellDropdown = True
        .InputTitle = ""
        .ErrorTitle = ""
        .InputMessage = ""
        .ErrorMessage = ""
        .ShowInput = True
        .ShowError = True
    End With

    Range("C8").Value = ""
         Range("D8").Select
         
 End If
    
End Sub