To use the 180 + 10 perk, you must have the actual
DVC reservation number. As vicki_c posted, if that number isn't on your RCI documents or you do not recognize it, call Member Services. (Ask for someone who works with the RCI exchangers - I believe they have a small group of CMs who are especially knowledgeable in this area).
Once you have the reservation number, go to
www.mydisneyexperience.com
Sign in or register (if you don't already have an account) and if your DVC reservation does not show up, use the feature to link your reservations. Once that's done, you should be able to make the 180 + 10 ADRs once your 180 day mark arrives.
Good luck!
P.S. You can also call MS to make your ADRs if you are unable or not interested in doing so online.