Sub teilstring()
    Dim raZelle As Range
    Dim strAdresse As String
    With Columns("B")
        Set raZelle = .Find("K*", lookat:=xlPart, LookIn:=xlValues)
        If Not raZelle Is Nothing Then
            strAdresse = raZelle.Address
            Do
                Cells(raZelle.Row, 2) = "K"
                Set raZelle = .FindNext(raZelle)
            Loop While Not raZelle Is Nothing And raZelle.Address <> strAdresse
        End If
    End With
End Sub

Sub teilstring2()
    Dim loZeile As Long
    With Columns("B")
        For loZeile = 1 To IIf(IsEmpty(Cells(Rows.Count, 2)), Cells(Rows.Count, 2).End(xlUp).Row, Rows.Count)
            If Left(Cells(loZeile, 2), 1) = "K" Or Left(Cells(loZeile, 2), 1) = "V" Then Cells(loZeile, 2) = Left(Cells(loZeile, 2), 1)
        Next loZeile
    End With
End Sub