It's not showing up in my account directly, but:
--I went to https://www.marriott.com/loyalty/member-benefits.mi and clicked on "view benefits"
--which took me to https://www.marriott.com/loyalty/mem...num-premier.mi
--where I signed in
--and that took me to a page that congratulated me and told me to choose my award.

I didn't choose, so it might have booted me out had I done so, but it's worth trying if you think you should have a link in your account but don't. (Actually, I went to the platinum page first and it told me I had to choose 50 night before 75 night....)