In Office 365, user passwords can be reset using the Admin Shortcuts. To reset password for a user in Office 365, login to the account then click the Admin link available at the top of the page. Navigate to Admin Shortcuts and click on the Reset User Passwords link.
Select the user to reset the password and click on the Reset password link. The following Send results in email will be displayed. To receive the changed password details, mark the checkbox with label as Send email and enter the required email address.
The next screen will display the temporary password for the username. When you first time login with that user the following Update password screen will be displayed requesting the user to create a new password.