To access your Premium features, follow the steps in this manual: https://community.windy.com/topic/11832/what-to-do-if-you-can-t-access-your-windy-premium-features.
Note that the restoration process has to be followed on the device you originally placed an order.

Once you have Premium active and you are logged into the device on which you are originally subscribed, log into your other device and Premium will be available there as well.

If the restoration fails, please, let me know in which step it failed and if there was an error message.