Details are yet to be posted on the Amex website. From their email:

Earn double the points

For the next three months, you’ll earn double points across your spend. From daily essentials, to online shopping and even when ordering in. That’s 4.5points for every dollar spent, except for government spend where you will earn 2points, up until 20July2020.

With no expiry and no cap on the amount of points you can earn each year, your points will accumulate regardless of how much you spend. So they’ll be waiting and ready for you to use, whenever you’d like.

Enjoy double the value when you Select+Pay with points

Additionally, for the next three months you can enjoy double the value of your points. By using Select + Pay with points to pay or part-pay for any eligible item on your Card statement with your Membership Rewards points, you’ll now enjoy twice the value.

Select + Pay gives you the freedom to pay for almost any item on your Card statement with points, including your annual fee – and now they will go twice as far. From your electricity bill to your weekly grocery shop, it’s easy. Simply select an eligible transaction on the Amex App or your online statement and select to pay with points.

Thank you for your Platinum Membership. Our thoughts are with you and your families. We will stay in touch as we work through additional ways to support our customers and communities.