Macro to match left string

Try this

Option Explicit
Sub del_6dig()
Dim i As Long, lrow As Long

Application.ScreenUpdating = False

With Worksheets("Data")
    lrow = .Range("A" & .Rows.Count).End(xlUp).Row
    For i = lrow To 2 Step -1
        If Left(.Range("A" & i).Value, 6) = "6digit" Then .Rows(i).Delete
    Next i
End With

MsgBox "Done"

Application.ScreenUpdating = True

End Sub