Option Explicit
Sub foo()
Dim lr As Long, i As Long
lr = Range("A" & Rows.Count).End(xlUp).Row
For i = 2 To lr
If InStr(Range("B" & i), Left(Range("A" & i), 1)) > 0 Then
Range("D" & i) = "OK"
ElseIf InStr(Range("B" & i), Mid(Range("A" & i), 2, 1)) > 0 Then
Range("D" & i) = "OK"
ElseIf InStr(Range("B" & i), Mid(Range("A" & i), 3, 1)) > 0 Then
Range("D" & i) = "OK"
ElseIf InStr(Range("B" & i), Right(Range("A" & i), 1)) > 0 Then
Range("D" & i) = "OK"
Else: Range("D" & i) = "KO"
End If
Next i
End Sub