The application administrator within your organisation can reset passwords for all users, if you do not see the 'Users' in 'Settings' your user does not have the correct authorisations.
Go to the Campaign Manager and log in with your credentials.
Select Settings.
Click on Users.
A pop-up is shown for SMS authentication.
Search for the user whose password you want to reset.
Select the user.
Fill in a new password (note: you must use a strong password).
Click on save.
The user can now login with their new password.
Users will automatically be asked to change their password once every 6 months.