If you have been gifted a Vegas World VIP or Elite Pass, look in the Misc section of your Outfit Items to find and activate it (it's a little hidden away).
Click "Vegas World" in the upper left corner of the Vegas World display.
The "Vegas World" button will change to a "Profile" button. Click it. (So you end up clicking twice in the same spot.)
Your Profile will open, and you'll see Outfits as one of the choices across the top of the window.
Click the Outfits button to open your Outfits
Click the Items tab to open Items
Select the MISC section (looks like a dresser and is at the very bottom) to find your membership Passes and USE them.