Bonsoir
modifies le début de ton code
With Worksheets("Feuil1")
'en colonne C à partir de C5
'Set Plage = .Range(.Cells(5, 3), .Cells(5, .Columns.Count).End(xlToRight))
Set Plage = .Range(.Cells(5, 3), .Cells(5, .Columns.Count).End(xlToLeft))
.Rows(.Range("B" & Rows.Count).End(xlUp).Row + 1 & ":" & Rows.Count).ClearContents
End With