If this option isn't present, then the option to use passwords has been disabled. If you need to re-enable it to clear out the password on a team, go to the TeamRaiser List and click Edit next to the event, click on step 4. Select Team Options then check the box next to Password-Protect Teams.
Alternatively, you can reach out to the Team Captains and explain that the functionality has changed and request that they change their password by making it empty and saving it.
The can update the password by following this documentation: http://help.convio.net/site/PageServer?pagename=User_TeamRaiser_TeamCaptain_AssignPassword_default