If you are a certain card level at your local casino, you qualify to upgrade to diamond if you show your card from that particular casino to the total reward club. You have to click on "see eligible programs" in your email, click your state, and then see what card levels at your local casinos qualify for diamond upgrade. I qualify from 2 local casinos southern california I play at often (only had to show 1). I am now Diamond with total rewards.

The email...

"FREE DIAMOND UPGRADE OFFER
Monica, for a limited time only, present an eligible loyalty card from select Caesars competitors at any Total RewardsŪ Center and receive a Diamond status upgrade through January 31, 2019. To learn how to maintain your Diamond status, see Tier Credit requirements here. Click below for a list of all eligible competitor tier levels.