Welcome to Insiders! Sometimes the special rates are property or region specific. Is the rate promo code in your reservation confirmation? If so, you can try that code in the Palm Springs location of your choice.
What you can also do is look for property availability in the Palm Springs area on the dates you want to go. When the hotel listing shows for all the available properties, just next to the number of the hotel (1.2.3.etc.) you can click on the hotel name and it will take you to the hotel's web page. You can click on the one you want to stay in. On that hotel home page you can click on 'Find: Deals and Promotions' and all the available deals for that property will display for you.
Hope this helps!