For setting up a 'sub-admin' who can change passwords, duplicate the default teacher role, and check Allow on the : Update user profiles
permission for the new role. Check the risks icons and make sure you are ready to assume them.
More:
http://docs.moodle.org/en/Capabilities/moodle/user:update
Roles and permissions
Allow certain teachers to change student passwords
This discussion has been locked so you can no longer reply to it.