Другое решение без l oop:
Public Sub StripLastName()
Dim strLastName As String
Dim LastRow As Long
'Create a with statement including the worksheet you want work with
With ThisWorkbook.Worksheets("Sheet1")
LastRow = .Cells(.Rows.Count, "A").End(xlUp).Row
.Range("C2:C" & LastRow).Formula = "=TRIM(RIGHT(OFFSET(C2,0,-2),8))"
End With
End Sub