Notify app data backup
Notify app respects your privacy and doesn't save your data on cloud. This is why you have to export a backup file if you want preserve your data when you change/format phone.
App creates automatically a backup file every 2 days (called auto backup) to ensure there is always a backup available.
If you are using a Mi Band 2 device, you can try also force resync last 15 days data (if still available on Mi Band) following this tutorial http://miband-mc200x.rhcloud.com/help/miband2_sleep_resync.php
I'm working to add an automatic Google Drive backup feature, to allow save automatically the backup on your account. This will allow restore data even if you lost or damage phone.