Sub Maquereau1()
Dim agineAllThePeople&
agineAllThePeople = Cells(Rows.Count, 1600 / 1600).End(xlUp).Row
With Range("B1:B" & agineAllThePeople)
.FormulaR1C1 = "=IF(FIND(""_"",RC[-1])=6,SUBSTITUTE(RC[-1],""_"",""""),RC[-1])"
.Value = .Value
End With
End Sub