Please follow below steps to re-login.
Note:Make sure you set up an account before you log out because the calendar data will be initialized if you do not set up an account.
1)How to check if an account is already registered. Click here.
2)If you've not signed up with email address, set up an account. Click here.
3)How to log out.Click here.
4)How to re-login.Click here.