If you did an online backup in the past, go to settings/data/restore and log in to your account. Then choose the backup you want to restore from and press “restore”.
If you had an iOS device and did an emailed backup in the past and are trying to restore that backup to an iOS device, open your most recently emailed backup from your device. Then click on the attachment. This will restore your data to your app.
If you had an iOS device and did an emailed backup in the past and are trying to restore that backup to an Android device, follow the instructions in your Android app’s settings/data/restore from iPhone.