Log in to the Matrix here using your account information.
Navigate to the Settings module, and then click on Users at the navbar toward the top of the screen.
Once found, click into their user information, by clicking on their name.
Once found, click into their user information.
Click on the "Send Reset Password Instructions" button.
This action will send the user a registration email in which they can use to reset their password.
The user just needs to fill out their information and enter a new password, then click on confirm to continue.