By default, subscription Photo Prints use the subscription's shipping address. To send them to a different address, follow these steps:
iOS:
Tap "Settings" (gear icon) from your active subscription
Scroll to the "ADD-ONS" section and tap on your Photo Prints
Tap "Shipping address" at the bottom
Select the new address or add a new one
Tap "Done"
Android:
Tap "Settings" (gear icon) from your active subscription
Tap on your "Photo Prints"
Scroll down and tap on the "Shipping address"
Select the new address or add a new address by tapping on "+ Add Address"
Tap "Done"