Warning! All data on watch will be lost!
1) Open watch Settings menu, choose System item and select Reset option
2) Uninstall and reinstall the official Mi Fitness app
3) Login on the official Mi Fitness app using your email and password
4) Pair the watch on the official Mi Fitness app
5) Uninstall the official app
6) Optionally, reinstall the Notify app
7) Pair the watch on Notify app by getting the new authkey code by following the automatic procedure