You will find a password option in the setting, select it.Once you are logged in, go to settings.Sign into office 365 which is operated by 21Vianet using your username and password.This option to change outlook password is to be selected if you have access to your old password but, wish to change it for some external influences or circumstances. The options provided to you to facilitate a password change will be: –
With the aforementioned reasons, you will have to select an option as per your needs.
How to Change Outlook Password in Outlook 365?