Greetings Sir or Madam and welcome to JA! I will do my very best to assist you with your problem.
Since you don't have the small piece of plastic to remove, you have to take the trim cover off from around the shifter and try to manually over ride the shifter. If this still doesn't work, you may have a broken piece on the shifter itself.Here is a diagram of the piece that normally breaks and needs to be replaced. Hope it helps!
i have an appt. this morning. i will get back to you this afternoon. thank you.