To restore the Premium account on a new device, you must first access the store (App Store or Google Play) from which the app was downloaded with the same account used for the purchase, then follow the procedure to recover the premium account from the app.
N.B. It is not possible to restore the premium account if you intend to do so on a new device with a different operating system than the one used when the Premium account was purchased.
E.g., if you purchased Premium on an Android device and then switch to an iOS device (and vice versa), it will not be possible to restore Premium on your Sticker Master account.