I found this link for Platinum and PP members where you can select your gift online. Personally, I picked the 5 suite awards Marriott Rewards I assume that when you reach the 75 nights in 2018, then you get the second link to select another award. Congrats to all the P and PP members! I hope that it helps to all those loyal members
Choose one from the following: five Suite Night Awards™, give the gift of Silver Elite status, 40% off your favorite mattress, five Elite Night Credits or a $100 charity donation.