If you're already logged in but need to update your password, click on your avatar in the top right corner of your screen. In the dropdown, select "Log out". When you're redirected to the login screen, select "Forgot Password" at the bottom.
If you aren't logged in and need to update your password, simply go to dash.callmargo.com. If you aren't logged in, select "Forgot Password" on the login screen.
A dialog box will pop up allowing you to enter a new password.