You can force a user to reset their password next login for going to the Users & Groups area, selecting a user and select "Edit"

Once selected go to the "Edit Password" tab and set the "Force password change on next login".

Once this is set the user will be forced to change their password when they next login. If the user fails to change their password they will be logged out.

If the user successfully changes their password the setting will be reset and they will not be asked again.