Firstly, only the user with Client Administrator Role or Super Admin can reset the other users password. Also, the current logged in user can modify its own password.
Apply following actions:
Navigate to User List View Under Administration Node
Make sure it is in the EDIT mode, if not , Click the EDIT button on the top left side
Click the Reset User Password button and press the Save and Close button.
(optional) If user want to reset its own password, tick the checkbox of Change Password On First Logon.
Finally, it will reset this user password to (blank)