Option Explicit

Sub Find()
    Dim fDate As Range, iDate As Variant
    Application.ScreenUpdating = False

    iDate = Format("mmm-yy")
    Set fDate = Sheet1.Columns(2).Find(iDate, , xlFormulas, xlWhole)

    If fDate Is Nothing Then
        MsgBox iDate & " не найдено", vbExclamation, "Ошибка"
        Exit Sub
    End If

    Sheet1.Activate
    fDate.Select
    ActiveCell.Offset(0, 1) = ActiveCell.Offset(0, 1) + "Yes"

    Application.ScreenUpdating = True
End Sub